Radio Broadcast - 1927, October - 81 Pages, 8.1 ... - VacuumTubeEra

RADIO BROADCASTOCTOBER, 1927WILLIS KINGSLEY WING, EditorKEITH HENNEYEDGAR H. FELIXVol. XI, No. 6Director of the Laboratory Contributing Editor.Practical Radio Construction and Repairing, by Moyer and Wostrel WILLIS KINGSLEY WING.AMO7S[G OTHER THINGS.. .Cover- - - -Design From a Design by Harvey Hopkins DunnSO MUCH is now being accomplished in the complete setfieldFrontispiece The Most Powerful Broadcasting Station in the World beginning with this issue, RADIO BROADCAST340will devote much of its space to reflecting the technical and otheradvancesNow You Can Receive Radio- - being made. The policy of this magazine remains asPictures Keith tienney 341before, to present the news of radio surrounded by as much asThe March of Radio An Editorial Interpretation 344possible of what the technical radio worker refers to as "dope."And much "dope" there is in this complete set side of radio asModern Radio Receivers are a Good InvestmentThe Month in Radiomany articles which will appear in following issues will strikinglyThe Danger of Direct Advertising on the AirListening to World-Wide Broadcasting is Licenses and What They Meandemonstrate. In all the other fields of radio endeavor whichNearThe Columbia Broadcasting ChainRADIO BROADCAST has covered heretofore the constructionA Profound Study of Radio Lawof radio receiving apparatus, laboratory experiments, shortwaveThe 1928 "Hi'Q" Has an Extra R. F. Stage - John B. Brennan 348communication, broadcasting from the technical andprogram side, and many others which we have covered toManufactured Receivers for the Coming Season - - -the satisfaction of our351readers, RADIO BROADCAST will be asactive as before. The expansion in1928 Radio Receivers of scope of our text pages is-Beauty and- - - - -Utility 352directly designedThe Neutrodyne Group,,.,,,, keep our readers in close touch with allsides of radio.354- -Servants of Your Light Socket- -356A"\ /"HERE is theRadiolas ,,,,,, experimenter who has not read of thefor 1928 j^gW rapid progress of the transmission of photographs bywire and radio and hoped that he would soon be able to sharein theSome New Offerings for the 1928 Season fascination of this new and intensely modern field? For360the past few years, RADIO BROADCAST has watched the progress-A New Regulator Tube James Millen of the art, hoping that devices would be developed within the363scope of the amateur laboratory and pocketbook. The leadingarticle on- - -The 1928 "Equamatic" Receiver- - -page 341 describes the backgroundJulian Kay 364Cooley"Rayfoto" system which inA New very few weeks will be madePrinciple of R. F. Tuning David Grimes 367through the pages of RADIO BROADCAST to the homeexperimenter. To be able to construct a radio photographBook Review ceiver for less than-Car! Dreher 369$100 should appeal very strongly to theUsing Radio in Sales Promotion, by Edgar H. Felixexperimental fraternity who are crying for something new to do.Here, in a manner of speaking, it is.1928 Loud Speakers - , , , . , j^oShould the Small Station Exist? John Wallace 372"The Listeners' Point of View"MANY pages of this issue are devoted to showing theofferings of the set makers for the coming season. LaterYour A. C. Set- -Edgar H. Felix 374issues of this magazine will describe in greater detail interestingtechnical features of these many receivers from many manufac?As the Broadcaster Sees It -Carl Dreher 376turers.Home-Constructing Transformers and Chokes for Power-Supplyr T" >HOSE of a technical turn of mind will read with great- -Devices Homer S. Davis 379J. interest David Grimes' story on page 567 describing the"Radio Broadcast's" Laboratory Information Sheets theoretical features of a radio- - - - -receiving system which is one cf388the most interesting that has come to our attention in manyNo. 109 The Type 874 Glow TubeNo. 133 Care of Power Supply Unitsmoons. Articles toNo. 130 Data on Honeycomb CoilsNo. 134 Loud Speaker Hornsby Mr. Grimes will describe theNo. 131 Resistance-Coupled AmplifierNo. 135 Closely Coupled Circuitscircuit constants and practical information about the system.No. 132 Resistance-Coupled Amplifier Circuit No. 136 Carrier TelephonyManufacturers' Booklets Available- - - -394THE Federal Radio Commission is making every effort topopularizeWhat Kit Shall I Buy? - 396A Key to Recent Radio Articles .*.. expression "frequency in kilocycles""wavelength in meters." It ishard going for some, but doing one's thinking in kilocycles does398remove many serious complications from calculations. Ever since"Radio Broadcast's" Directory of Manufactured Receivers - -402its August, 1915, issue RADIO BROADCAST has standardized theuse of kilocycle designations, always printing at the same time,Making Radio Installations Safe Edgar H. Felix 410equivalent wavelength in meters. We are in sympathy withthe wishes of the Radio Commission and invite theBook Review-expression416of our readers on this subject.=*Doubleday, Page & Co.MAGAZINESCOUNTRY LIFEWORLD'S WORKGARDEN & HOME BUILDERRADIO BROADCASTSHORT STORIESEDUCATIONAL REVIEWLE PETIT JOURNALEL EcoFRONTIER STORIES"WESTDoubleday, Page & Co,BOOK SHOPS(Books of all Publishers)I LORD & TAYLOR BOOK SHOP\ PENNSYLVANIA TERMINAL (2 Shops)NEW YORK: -/GRANT CENTRAL TERMINALJ 38 WALL ST. and' 5^6 LEXINGTON AVE.848 MADISON AVE. and 166 WEST 32NDST.ST. Louis: 223 N. 8TH ST and 4914 MARYLAND AVE.KANSAS CITY: 920 GRAND AVE. and 206 W. 47TH ST.CLEVELAND: HIGBEE Co.SPRINGFIELD, MASS.: MEEKINS. PACKARD & WHEATDoubleday, Page & Co.OFFICESGARDEN CITY, N. YNEW YORK: 285 MADISON AVENUEBOSTON: PARK SQUARE BUILDINGCHICAGO: PEOPLES GAS BUILDINGSANTA BARBARA, CAL.LONDON: WM. HEINEMANN LTD.TORONTO: OXFORD UNIVERSITY PRESSDoubleday, Page & Co.OFFICERSF. N. DOUBLEDAY, PresidentNELSON DOUBLEDAY, Vice-PresidentS. A. EVERITT, Vice-PresidentRUSSELL DOUBLEDAY, SecretaryJOHN J. HESSIAN, TreasurerLILLIAN A. COMSTOCK, Asst. SecretaryL. J. McNAUCHTON, Asst. TreasurerOOUBLEDAT, PAGE & COMPACT, Garden Qity,X[ewCopyright, 1927, in the United States, Newfoundland, Great Britain, Canada, and other countries by Doubleday, Page & Company. All rights reserved.TERMS: $4.00 a year; single copies 35 cents.338

RADIO BROADCAST ADVERTISER 339Lata Balsa ReproducerModel 150, Price $50THEstrides made in thepast few years by thebroadcasting stations inbettering the quality of theirtransmission have been remarkable.The same principles havebeen applied to the phonograph,resulting in the new recordsand machines which aremiles in advance of the oldertype.These improvements are nowavailable to every listener-in.However, there are some radioreceivers which will not reproducethe wonderful music being broadcastby the improved stations.By applying the same principlesto radio receivers which haveproved so helpful in the broadcastingand phonograph fields itis now possible to make the mostout of the broadcasting. By utilizingthe scientific aids now availableold and new receivers may bemade to produce music which inevery way resembles the original,There is asmuch difference between this new form of reproductionand the old as there is between the newphonograph and the old scratchy, squawkycylinder machine of yesteryear.Resistance coupling simplifies receiver amplifierconstruction and greatly reduces the cost. It isrecognized by leaders in the search for the besttone quality as being the ideal amplifying system.It permits the passage of the very low notes andthe very high ones with the same ease. It bringsto the loudspeaker a true but greatly amplifiedpicture of what is picked up from the broadcastingstation.There is little use in having this wonderfulARTHUR H. LYNCH, inc.General Motors Building1775 BroadwayNEW YORK CITYSole Sales Representativesthing available if we do not make use of it.can now be utilized very simply. Radio artists,editors and many musicians have expressed bothpleasure and amazement on hearing the toneportrayal of symphony orchestras, as well as jazzbands which Nature's Sounding Board has madepossible.Nature's Sounding Board is known as the LataBalsa Reproducer. It is more than a "loudspeaker." It is science's latest contribution tothe musical art. It will make any good radio receiversound much more natural and pleasing.Lata Balsa Reproducers are available in completed,Everything necessary for the building of amodern three-stage resistance coupled amplifierwhich may be applied to any receiver.59.00artistically decorated models ranging inItprice from $30. to $50. Kits arealso available in two sizes. The famousLata Unit, or electrical drivingmechanism is now ready fordelivery and is ideal for use withthe Lata Balsa Reproducer Kits.The accompanying illustrationwill give you some idea of the attractivenessof the reproducerto realize its superior tone qualityyou must hear it.The Lata Balsa Kits are completeand may be assembled in a very short time byanyone. No mechanical skill or electrical knowledgeis required to follow the simple instructions.Once you haveheard this wonderfulreproducerno otherwill satisfy you.The coupon belowis for yourconvenience inordering. Use ittoday and youwill never regretit.RETURN THIS COUPON-ARTHUR H. LYNCH, Inc.General Motors Bldg. 1775 BroadwayAt 57th Street, New York CityGentlemen:Please send me the items checked, for which I enclose mymoney order or cash, also information on prices and sizes ofArt Models of Lata Balsa Reproducers.Name.Lata Balsa Reproducer Kit, 13 JC 24 $ 8.00"21 X36 10.00Unit 8.00Lynch Resistance-Coupled Amplifier Kit . 9.00Address. . . .City-StateThe number 2 Lata Balsa Kit and Reproducerunit assembled. You can duplicate this assemblyin a very short time by using this kitand complete instructionsBALSA WOODREPRODUCER, Corp.331 Madison AvenueNEW YORK CITY

THE SMOST 'POWERFUL ^BROADCASTING STATION IN THE WORLDview of the transmitting panel of the 100-kilowatt transmitter at the South Schenectady laboratories of the GeneralElectric Company. Experimental programs are sent out with this set, using the standard wavelength of WGY, frommidnight to one a. m., Eastern Time. The transmitter went on the air August 4th, marking the first time that power as greatas 100 kilowatts has been used in broadcasting. The three water-cooled 100-kilowatt tubes in the foreground have an attachmentfor clearing out the gas from the tube 'while it is on the panel

RADIO BROADCASTVOLUME XI NUMBER 6OCTOBER, 1927NOW-You Can Build Your Receiver for Less Than One Hundred DollarsBy KEITH HENNEYDirector of the LaboratoryHow It WorksIf II WERE is an undeniable thrill in witnessingI an extraordinary scientific event, such as-^- receiving one's first broadcast program, orin talking across the Atlantic for the first time,or in seeing photographs that have been sent byradio from England, or in talking via short-waveamateur radio with a fellow "ham" on a steamshipa thousand miles up the Amazon river. Infact, as the French astronomer, Camille Flammarionsays, "Unless one has a stone instead ofa heart and a lump of fat in the place of a brain,it is difficult not to feel some emotion over theachievements of science."The writer's first contact with Austin G.Cooley, who has been responsible for the picturetransmission system to be described in RADIOBROADCAST, produced one of those technicalthrills. Cooley was working down in the "shack"at 2 GY, the short-wave station of the RADIOBROADCAST Laboratory, a small place withscarcely room enough to stow his extensive gear.On one bench was a metal drum on which aphotograph of a young lady with a large andfloppy hat turned over and over. On the otherside of the "shack" was another rotating drumcovered with photographic paper with a smallspot of light playing on it, and filling the shackwas an undefinable sound like that of a highspeed motor whirring away with whining andsomewhat obnoxious tone. In two or three minutes,Cooley stopped the motor, took the photographicpaper from the receiving drum, developedit in rather dim daylight, and there was theyoung lady again, hat, white plumes and all.Between the transmitter and receiver was anartificial telephone line 300 miles long so that forall practical purposes the young lady's picturehad been sent to Garden City from, say, Washington,D. C.Since that time, Cooley has produced severalpicture systems, one of which is applicable topresent wire telegraph channels so that facsimilecopies of original messages may be transmittedat a cost not exceeding present rates. Anothersystem the one in which we as radio experimentersare interested has been developed tothe extent that with a not very expensive attachmentto the ordinary radio set, one can receive athome photographs, letters, telegrams, pictures,or text torn from newspapers. This system isknown as the Cooley "Rayfoto."These radio-transmitted pictures are comparativelygood reproductions, quite satisfactoryworked under great odds, trying to send pictureExpedition 1926 Cooleywhen one considers the simplicity of the apparatusMacMillan in when transmits its form of intelligence on it. In a wayand the compromises which were necessary signals by short waves back to the United States.in order to obtain them, it must be remembered This background is necessary to understand thethat it is about seven years since the first small years of effort that have gone before the presentgroup of amateurs heard the human voice, and development. This development has been slow,music, coming in by wireless. The early poor and full of disappointments but the final resultquality of reception must not be forgotten; nor has been that his systemis workable, comparativelymust we lose sight of the fact that it has takensimple to operate, and what is more im-since 1835, when S. F. B. Morse performed his portant in the eyes of the average experimenterepoch-making experiment of transmitting slowit is inexpensive.and uncertain telegraph signals via wires, to sendTHE LURE OF HOME EXPERIMENTmessages at the rate of several hundred charactersper minute.The Cooley pictures are better than most of WHY should one want to receive pictures byradio at home? As well ask: Why havethe static-laden ones that have come across the thousands of experimenters built receivers forthe reception of music, or code? In this, therehasQ always the thrill of accomplishment;Radio pictures at home that's making something with one's hands, somethingwhat the that works:experimenter has beenSecondly, there is the hopein everyone's heart that television, the art ofwaiting for. Now it is possible. transmitting scenes from life itself by wire orFor less than $100, you can build radio, shall become practical within his time.Before television shall be anyo'ur own picture receiver, connectaccomplished fact,we must conquer the idiosyncrasies of the transmissionof still life pictures, an art known asit to your broadcast set and jumpinto a new and fascinating field oftelephotography. By introducing legions of experimentersexperiment. Exclusive articles ingeneral problem of sendingand receiving pictures by radio or wire, CooleyRADIO BROADCAST in the Novembermay have a share in advancing the day when thenumber and in following issues more difficult task of committing moving pic-tures to the ether shall be solved. The amateurwill tell you bow to build andhas been thanked by engineers for his persistenceoperate the receiver.developing short-wave channels; many havesaid that to him alone belongs the credit for advancingthe art of communication by the use ofAtlantic. Some of them are reproduced here. those very high frequencies. At any rate, he hasImprovement in detail and shading of the Cooley had his share in making possible communicationRayfoto pictures will come. The important fact isby short waves across vast distances with inexpensiveapparatus. Who knows what his sharethat here is something the experimenter can havefor his own and can have the sport of developinghis experience as this apparatus is improved andrefined.may be when the ultimate success of telephotographyand television has been achieved?The transmission of a picture by the CooleyTo know the Cooley apparatusis to know system differs from the transmission of musicCooley, to visualize the young M. I. T. student in one important respect: it takes a single audiowho preferred his own researches into the then frequency and performs tricks on it which at theunknown field of picture transmission to the prescribedreceiving end are translated from sounds to otherstudies with the result that he was effects which influence a photographic paper.dropped from the college register during hij For example, good broadcasting requires that afourth year; his long nights of work, sleeping band of frequencies 10,000 cycles wide shall bewhen sleep was necessary beside his apparatus transmitted. These frequencies at the receiver areon a laboratory bench. One should know of reconverted to sound waves. The picture systemtwenty-four-hour days in the Arctic on the takes a given frequency, say 1000 cycles, and

342 RADIO BROADCAST OCTOBER, 1927it is less complicated than broadcasting music; inother ways broadcasting pictures is more complex.The broadcasting station which may electto transmit pictures as well as music or speecheswill use its present equipment. Since picturesaccording to the Cooley system are first translatedinto sound impulses and since the phonographrecord is a means of recording for futureuse such sound impulses, thereby defeating twoof nature's limitations, time and space,[the broadcastingstation that will invest in a phonographturn-table needs no other equipment to fill theether with pictures.AUDIO AMPLIFIER.-CORONA" COILOSCILLATORWIRE FROM END OfCORONA" COIL TO NEEDLE POINTPOINTREVOLVINGDRUM[PICTURE BEING RECEIVED ONPIECE OF PHOTOGRAPHICPAPERYOUR REGULAR RADIO RECEIVER ISUSEDTHOSE who will receive pictures will usetheir present broadcasting receiving set whichshould be equipped and operated so that overloadingand severe distortion of other sorts do not occur.As in transmitting sounds, distortion at thereceiving end produces an unintelligible or garbledreproduction. The receiver must be within the"service area" of the transmitter that is, insidethe distance at which fading takes place; the operator must be able to develop and fix ordinary developing-outpaper, such as Azo, Velox, or otherpapers with which the amateur photographer isalready well familiar. Here is an opportunity forthe radio enthusiast who has dropped his photographichobby to bring developing trays from theattic, and to renew his acquaintance with hydroquinone,metol, HQ, and hyposulphite of soda!The present simplified system transmits andreceives original photographs full of strong contrast,such as newspaper photographs, or thosein which a loss of detail will not mar the recognizablefeatures of the transmitted picture. Theexamples reproduced here will give an idea ofthe work that can be done. These limitationsare largely due to the simplification of thereceiving equipment, and, as experimenters becomemore familiar with the present apparatus,more refinements will naturally follow, refinementswhich will make it possible to receivegreater detail, and naturally better pictures.The process of getting the picture into theether is not too complicated for anyone to understand.The picture iswrapped around an aluminumdrum which revolves in front of a verystrong light. As the drum revolves it moves alonga shaft, so that the beam of light eventually hasPicture to be sentis wrapped aroundthis drum "LSPRINGRELAY TORELEASE DRUM >--*' SPEED REGULATORTO WINDMOTORRADIO BROADCAST PhotographTHE COOLEY "RAYFOTO" RECEIVERSimplicity is the keynote of the Cooley picture transmission system. Signals in the form of an audiofrequency tone enter at the point marked on this photograph, are amplified in a single-stage transformer-coupledamplifier, after which they are placed on the oscillator circuit through a modulationtransformer not visible here. The signals in the oscillator circuit drive the corona circuit whose outputis conducted to the rotating drum and photographic paper by the wire and needle point shown here.The drum is rotated by the familiar spring motor which usually turns phonographic records. Themilliammeter, which is essential, usually reads the oscillator currentcovered the entire picture, illuminating a smallbit of it at a time. The light which is reflected bythe picture passes into a sensitive photo-electriccell, another of modern science's marvels. Whenthe beam of light falls on a black portion of thepicture, most of the light will be absorbed andlittle reflected and consequently what passes intothe photo-electric cell will be small just as thepart that comes to the eyeis small; which explainswhat we mean by the word "black."This sensitive photo-electric cell, whose historydates back many years and touches the livesof many famous scientists, consists of a potassiumplate and a second metallic electrode whichhas a battery attached to it maintaining it at apotential positive with respect to the potassium,Apieceof photographicpa peris wrappedaround this drumHOW THE COMPLETE SYSTEM WORKSThe owner of receiving apparatus need not worry about how the pictures get on the air, but in case heis interested, here is a layout of the complete system, transmitter, waves in the ether, receiver and all!The switch at the right of the receiving equipment and the trip magnet are part of the start-stopsystem that insures synchronism between transmitter and receivermuch as the plate of a vacuum tube is maintainedpositive with respect to the filament bythe B batteries. When light shines on this potassiumplate, electrons, those omnipresent negativeelectrical charges, are given off, their passageto the second electrode toward which they areattracted constituting an electric current. Thisminute current, usually of the order of a fewmillionths of an ampere is greatly amplified andinterrupted by another current of looo-cyclefrequency. The result is that what were originallyblack and white visual images have been translatedinto sound impulses which are then impressedon the radio transmitter, or a telephoneline, and are sent out like speech or music.At the receiving end the process must be reversed,i. e. sound impulses must be translatedinto light impressions, back into those originalblack and white spots. Assuming that nothinghappens in the intervening space, no static ispicked up, no fading has lost the signal, at thereceiving end the conventional broadcasting setmay be used, and if a loud speakeris attachedto the output of the receiver in the normal mannerwe should hear this varying note which isabout two octaves above middle C on the piano.WHY LOCAL AMPLIFICATION IS NEEDEDMOST cases it will be necessary to boost thisINwavering note to sufficient strength to operatethe rest of the translating apparatus which consistsof an oscillator, similar to that used in superheterodynereceivers except that its wavelengthis usually above the broadcasting band, andfinally what Cooley calls a "corona" coil. It willremind old-time electrical experimenters of theTesla coil, a device used to transform a.c. voltagesinto other voltages high enough to produceelectrical discharges across intervening space, inthis case about a quarter of an inch.Under ordinary conditions, the carrier of thetransmitter tuned-in but no picture being onthe air, the oscillator will be oscillating so feeblythat no corona is taking place, but when thesignal arrives it supplies power to the oscillatorso that a nice fat discharge is produced whose

OCTOBER, 1927 NOW YOU CAN RECEIVE RADIO PICTURES! 343RADIO BROADCAST PhotographsTHE COMPLETE RECEIVING APPARATUSHere is the entire receiving apparatus. The receiver in this case was a well known set operating from aloop, picking up signals on 208 meters which originated in another part of the Laboratory. They aretuned-in and sent through the picture apparatus which is described in greater detail in the otherphotographstotal cost of the apparatus, exclusive of batteries,tubes, and broadcast receiver will be less than$100. All of the electric apparatus can be madefrom material easily available to the experimenter.Complete descriptions by Mr. Cooley ofthis equipment and how to operate it will follow.A word about the availability of pictures.Inasmuch as the original equipment for a broadcastingstation need involve no more than theexpense of a phonograph, there is a certain sourceof these radio pictures in every broadcast station.Broadcast stations will find in the transmissionof the Cooley "Rayfotos" a sensational extensionof their activities and by the time thisarticle is in the hands of experimenters, and bythe time the receiving equipmentis ready, pictureswill be on the air. The Cooley systemisbeing exhibited at the New York Radio Showthis month.And there you are: Pictures by radio and inyour own home.SPECIAL MODULATIONTRANSFORMERintensity varies with the shading of the transmittedpicture.The counterpart of the rotating drum of thetransmitter will be found at the receiver. Here,instead of an electrical motor we use for sake ofsimplicity a phonograph turn-table which isgeared to a small aluminum drum around whichthe sensitive photographic paper is wrapped.The corona discharge sprays the paper from afine needle and in some way not well understoodaffects the emulsion of the photographic paper.Whether this is an electrical or chemical effect orwhether there is enough light from the corona toexpose the paper is not fully known.But for Cooley's purpose it does not matter.When developed, the paper shows black spotswhere the discharge was heavy; light spots wherethe corona was weak.Now in all picture systems, some means mustbe provided to keep the receiver in exact synchronismwith the sender; when the latter startsthe receiver must start, and not in the middle ofthe picture which as anyone can see would havecertain disadvantages! A simple scheme for holdingthe receiver and transmittertogether has beenemployed.It is known asthe "start-stop" system,and isvery simple and flexible.In operation the receivingdrum revolves slightlyfaster than the transmittingdrum and it therefore completesa revolution in aslightly shorter time. Atthe end of each revolutionthe receiver drum is held bya trigger until the transmittingdrum completesitsrevolution. A signal is transmittedthen that releases thereceiving drum so the twostart off together. The radioThe modulation transformer, which was -hidden in the view on page342 by the corona coil is shown here. All of the parts for this appara-signals are not strong tus have been especially designed, and will be available soon. A goodenough in most cases to idea of the gearing mechanism and of the width of the drum on whichoperate the trip magnet that the picture is received may be had from this photograph. The picturereleases the receiving drum may be as wide as the metal drum. The needle point actually ridesat the beginning of eachon the paper as is shown hererevolution so this magnetisoperated through a more sensitive relay.Both the trip magnet and relay can be seenin the picture of the apparatus shown on thispage. The single pole double throw switch Sis really part of the trip magnet. When the armatureof the trip magnet is against the stop on thedrum, terminals 2 and 3 on the switch are pushedtogether and therefore all of the energy from theaudio amplifier passes into the relay. When thesynchronizing impulseis received it activates therelay and the trip magnet thus releases the drumand also causes the switch S to make contactbetween terminal I and 2 and then all of theenergy passes into the oscillator.The present apparatus transmits 4x5 photographsat a rate of one and one-half inch perminute or a little over 3 minutes for a picture.The Cooley receiving apparatus consists offirst of all one's broadcast receiver, then certainmechanical parts which will be on the marketsoon, and then certain electrical apparatus whichany experimenter can build and operate. TheCORONA DISCHARGEOCCURS AT THIS POINTACLOSE-UPWHAT THE PICTURES LOOK LIKEThese photographs have been transmitted by theCooley Rayfoto system. Pictures may be fiveinches wide and about six inches long and a littleover three minutes for each picture is required.These pictures have not been retouched

THEModern Radio Receivers Are a Good InvestmentRadio World's Fair opens theradio season for the broadcastlistener. Fitting its significance, theFair is held in mid-September atthe huge Madison Square Garden in NewYork.No radio season has ever started moreauspiciously. Technical progress, representedby simple, easily operated andmaintained radio sets, many powered directlyfrom the electric light mains, withbroadened tonal range, bring the manufacturedreceiver to a standard so high thatrevolutionary change can no longer beexpected. Greater broadcasting programsand improved receiving conditions makethe possession of these modern receivers allthe more desirable.Every industry goes through the samecycle of growth; first, it has a discouragingstruggle for recognition, then a boomperiod with almost day to day improvement,and finally, stabilization, with slow,continued and healthy progress, keen competitionamong leaders and the gradualelimination of the less capable who thrivedonly during the boom period.In stating that radio has reached a slowerlevel of development and that the purchasermay now select his receiver with theconfidence that it will not be hopelesslyobsolete within a year or two,or even four or five years, we drawour conclusion from fairly simple andindisputable premises. Improvementof any device is a matter of renderingit so simple that no technical knowledgeis required for its operation, sorugged and self-sustaining that butlittle attention is needed to maintainit in good condition, and so pleasingin appearance that it harmonizes withthe most luxurious surroundings.High standards of simplicity havebeen attained in radio when we havemany receivers in which five circuitsare simultaneously controlled by onedial and calibrated so that stationsmay be promptly logged. The onlyperishableelements in some receivingsets now are the filaments ofthe vacuum tubes themselves whichneed be replaced perhaps onlyonce a year. In tone quality, radiohas reached a standard of reproductionfar above that which satisfied the phonographindustry after twenty years ofprosperity. This standard can be raised atwill with our present knowledge and facilities,although the cost of doing so is prohibitiveand the effect hardly noticeable to theaverage listener. As to appearance, there isstill room for some improvement by theattainment of greater compactness in themore powerful receivers, but models areavailable for which no apologies need bemade even in the most exacting surroundings.Radio has certainly not reached its limitof development. Improvementswill continuealways and this year's sets will alwaysbe better than last. Two or three yearsago, a radio receiver was but a one-yearinvestment for those who would possessthe best available in the market. This year'sstandards are making the latest and bestmodels perhaps a five-year investment inapproximately the best radio receptionattainable.It is a strange paradox that the substantialdevelopments in manufacturedreceiving sets are not more widely appreciatedby the technically minded radioenthusiast. From extensive contact withCOLONEL LINDBERGH INSCHENECTADY" Aviation and radio are twin sisters engaged in the joint enterpriseof overcoming time. Distances are no longer measured inmiles, but in hours, minutes, and seconds. Colonel Lindberghreduced the distance from New York to Paris from days tohours. Radio has brought all parts of the world into talkingdistance of the United States," said Martin P. Rice of theGeneral Electric' Company. Above: Martin P. Rice, and atthe extreme right Colonel Lindberghthe better informed element of radiolisteners, we have analyzed this lack offamiliarity as attributable in part to theexperimenter's preoccupation with theintricacies of set building and the failure ofthe radio set manufacturer to lay beforethis group, so invaluable to the building ofreputations, the real facts about the designand construction of his receiving set. Glitteringgeneralities about performance donot intrigue the radio experimenter who,in past years, has successfully excelled inthese proclaimed qualities with his homemadecontraptions.But a new day has dawned. The experimentercannot deny the superiority ofthe better manufactured sets. Already he isturning his attention to new fields. Whilebuilding radio receivers was still an experiment,the successful outcome of which dependedupon skill, ingenuity and patience,this hobby had no rival in the hearts ofthose who considered the soldering iron aninstrument of conquest. The element ofmystery is disappearing. Set building hasbecome the following of a well establishedformula. The thrill of accomplishmentstill exists but the procedureis so wellcharted that the joy of exploration anddiscovery is practically gone. These missingelements, which satisfy the experimenter'sinsatiable desire to overcomeobstacles and to conquer the unknownare being rapidly supplied by new linesof endeavor. Telephotography and,some day, television, internationalshort-wave broadcast reception, moderninstallations with remote controlof the radio receiver, laboratory experiments,home motion pictures,aviation, mechanical models and athousand one avenues of expressionbeckon the experimentally inclined.The pages which follow attempt toreflect accurately the trends in theinterests of our readers. The manufacturedreceiver deserves an increasingamount of attention, as do newfields of development like telephotographyand short-wave reception.We do not propose, in the least, toneglect the set builder, but ratherto keep him in touch with thelatest developments of the art. We

.. ...'OCTOBER, 1927 SHORT-WAVE BROADCASTS YOU CAN HEAR 345feel the broadened scope of our pages will number which may be accommodated tinction which will be recognized by theappeal to each of the three principal throughout the world. Receiving sets, legal profession as one of no small moment.elements of our reader audience, the experimentalgroup; those professionally in-necessarily of the regenerative type and phases of radio communication and inter-working on the high frequencies, are The book deals comprehensively with allterested in radio, ranging from dealer to consequently, at the present time at least, prets the Radio Act of 1927 in the light ofengineer to manufacturer; and the radio no vast number of receiving sets can use precedents already established by theenthusiasts who follow these pages to keep these channels without causing destructive Courts. The book studies exhaustively theabreast of progress in radio.interference. Undoubtedly, the radiation complex problems raised by the existenceproblem will be overcome, but fading and of broadcasting stations, although theListening to World-Wide Broadcastinguse of short waves in the essential local and by lack of established legal precedents andtransmission irregularities will prevent the author has been seriously handicappedregional broadcasting services.decisions on most vital issues. Clearly,to the development of broadcasting,experimentersSince short-wave stations practically many important legal questions which willPRIORreceiving cover the earth with their signals, it is feasibleassign but one powerful short-wave months are yet to be settled.harass the Courts during the next fewsets having a wavelength range offrom 200 to 25,000 meters, so that they broadcaster to a frequency. Consequently, The preponderance of evidence andcould eavesdrop on every available radio it is desirable to select a short-wave broadcastingband at once and allot frequencies one to conclude that the question ofprecedents which Judge Davis cites leadschannel. Experience has taught us tobuild more efficient receivers for much so as to meet the needs of all the countries confiscation of property, involved in cancellationof station licenses, is one which willnarrower ranges. Indeed the present of the earth. This matter should be consideredin the International Radio be decided against the regulatory power ofbroadcast band is the widest for which ahigh grade receiving set with easy control Telegraph Conference, convening in Washingtonin October, lest confusion and con-established stations, which find their ser-the Commission. On the other hand,can now be made. Many of the servicesconducted on non-broadcasting channels gestion arise later. There is no need for a vice curtailed by interference from newcomers,seem to have ample grounds forare gradually being rendered by radio great number of short-wave broadcasterstelephony rather than radio telegraphy. in any one country, and some means should securing restraining injunctions on theThe objection that laborious study of the be devised for limiting their increase before grounds of prior rights. Reading theseradio code isnecessary to listen to them is problem becomes as serious as the congestionnow obtaining on the conventional all the more that our suggestion that stationparts of the Judge's book leads us to regretthereby eliminated.Almost every day of the year, new radio wavelengths.priorities be recognized, was not embodiedservices open up. The possessor of a longwavepicks his signals from every A Profoundin the law. That was urged in these pagessection of the globe. AStudy of Radio Law long before the Radio Act was finallyslight movement ofdrafted.the dials may transfer his attention from a F I THE Law of Radio Communication by The author considers federal jurisdictionstation in Java to another in Iceland. There / Stephen Davis, former Solicitor of and its relation to state and local regulationare now nearly one hundred stations whichthe Department of Commerce, recentlypublished by McGraw-Hill, is tions, libel and slander, as well as the sig-of radio communication, copyright ques-can be heard in any part of the world.Perhaps the most important developmentof all, so far as the broadcast listener It has beena valuable contribution to radio literature. nificance of every phase of the recent Act.is concerned, is the increasing interest in awarded theI. GENERAL BROADCAST ADVERTISINGshort-wave broadcasting. 2 XAF, the 32- LinthicumA. Basic Rates for periods between 7:00 P. M. to 11 :00 P. M. Local Time.meter (gijo-kc.) Schenectady transmitter FoundationRED NETWORKBLUE NETWORKAvailable only at a GroupAvailableof the General Electric Company, is only at a Grantactually PrizeCharge Charge ChargeCiltMPer Hr. PerbyK Hr. Cl^tOfsupplying the world CitiftPlr Hr. Per with tt radio "Hr. F,, IA Hr.Charge Che.,,,K'ew York$600.00 $375.00 $234.38programs. the facultyBoston . 250.00 156.257.66 New York $600.00 $ 75.00 $234.38Its signals are Hartford .120.00 75.006.88frequently and regularly heard of law ofBenin . 25000 56.25 97.66120.00 75.006.88Worcester . 120.0075.006.88 Springfield 210.00.11.25 S2.03in England, South Africa, South America, NorthwesternUniver-Washinuton190.00 1J8.754.22Portland. Me.120.00 75.006.88.Philadelphia 310.00 193.751 1.10 Baltimore 190.0018.75 74.22New Zealand and Australia. An increasingRochester .' 200.00 25.00 78.13.Schenectady 190.00 118.754.22Buffalo .. ..200.00 125.008.13 Pittsburgh 300.00 87.50 117.19number of American stations,a dis-250.00 156.257.66casting their Total for Network. 11770.00 $2356.25 $1466.46 Total for Network. ..$2800.00 $1750.00programs on short wavelengths.British, German, and Dutch11087.52HOW MUCHSUPPLEMENTARY CITIESITstations are within range of AmericanCOSTS TOCharaeshortwavesets. Short-wave programs are BROADCASTSt. Lotiii ....(82.03 For me in conjvn,CM,,Per 14 Hr.readilyMinn. St. Paul82.03 the Rii or Bint Nttemk*heard at great distances Rate cards areduring the summerwhen the used in sellingprogram range of most standard "time"on thewavelength broadcast receivers is very air just asMIDWKSTKKN GROVPlimited. Several companies are already publishers useDavenport(190.0018.75DCS Moinei : 190.0018.75Omaha190.0018.75preparing to meet the demand rate cardsKansas City190.00 1875for shortwaveOklahoma City-Tuls 190.0018.75inDallas Ft. Worth . 190.0018.75sellingreceivers.Total for $445.32channel, placing a definite limit the overthe stationsThe questionpresent services. A short-wave transmitterit costs to sendfadingmay ariseskipwhether shortwavebroadcasting will not replace our tables showAvailable onlyNashville '... . 190.00 1875 74.22 For nte in conjunction witreSan"space."ratesPACIFICFranciscoinCOAST$300.00ThetheseNETWORK$187.50Croup $1140.00 $ 1 12.50SOUTHERN OBO :p$117.19Louisville $180.00 ) 12.50 $70.31atexactly whatgroupMcmphii 190.00 1 18.75 74.22 the Red or Blue Network*Atlanta 190.00 118.75 74.22is ideal for long distance transmission but,because of and a progr a mTotal for Croup $750.00 $468.75 $292.97the distance overtheentireeffect, is of little or no local service. Within United States.Selectively at-a,laHt Los Angeles 300.00 187.50 117.19Portland "150.00 3.7S 58.60mtlh San FnnfitcoSeattle200.00 125.00 78.1 3two hundred to six hundredAmiles of shortwavechargesstations, theirlarge partSpokane 150.00 93.75 58.60of theTotal for Network... signals are$1100.00 $687.50 $429.71usually are consumedinaudible but even moderate power deliversB. Basic Rates forin the periods other than between 7:00 P. M. 11:00 P. M. Local Time arehighone-half above rates."a strong signal for immense distances cost of thecounts on Basic Rate* for number of periods under contract not to exceed one yearbeyond the dead area. Hence special every highphone wires25atton:Less tkan 25 Nfrequency station requires an exclusive50 . 99 IScon necting100 . Z99broadcasting sity, Detroit 340.00 212.50Cleveland ..'.'.'...... 250.00 156.257.66including WGY, KDKA, WRNY, WLW, WAAM,Detroit 340.00 212.501 6.56Cincinnati '.7T! 250.00 156.25 97.6*Cincinnati 250.00 156.257.66WRAH and WHK are, or soon will be, broad-Chicago 460.00 287.50 179.69 Chicago 460.00 287.50 179.69126.56on 100 and

346 RADIO BROADCAST OCTOBER, 192,7For the time being, it is the only authorityavailable to the lawyer handling cases forbroadcasting stations. We hope, for thegood of radio, that Judge Davis will soonfind itnecessary to write a revised editionoccasioned by court decisions to the unansweredquestions which he so ably raises.His book thoroughly establishes JudgeDavis as the outstanding American authorityon the law of radio communication.The Danger of Direct Advertisingon the AirTHE United States Radio Society hassent us its literature, including acode of regulations and by-laws forlocal affiliated chapters of the society. Byfollowing these regulations, any local radioorganization may become affiliated in thenational group, and means are provided forrepresentation of each chapter in thenational deliberations. In absence of localchapters, a membership can be securedby individuals who may write Paul A.Greene, Managing Director of the Society,at the Temple Bar Building in CincinnatiOhio.The Society recently forwarded thereturns from a questionnaire to the FederalRadio Commission which emphasized theunpopularity of certain broadcasters permittingblatant advertising, particularlytwo well known nuisances in Shenandoah,Iowa. The St. Joseph, Missouri CommercialNews, writing of these "advertising stations,"says "one of the best known of thesenuisance stations reported, the first weekin February, that it had in a month soldabout 45,000 pieces of dress goods, amountingto approximately 175,000 yards.Figuring the mileage, this amounts to 99-jV miles of dress goods." Continuing, thearticle comments on the competition whichthis direct advertising offers to the smalllocal merchant.One of the claims made to theFederalRadio Commission by one of these stationswas that it lowered the price of goods to thefarmer. Refuting this claim, the St. Josephnewspaper says:One of the best known stations ,not far from St.Joseph, recently put on an active sale of cans ofsmoked salt for use in butchering on the farm. Itoffered two cans of a good quality of smoked saltfor $2.50, postage prepaid. Orders were acceptedfor not less than two cans. One Iowa farmer whofell for this great bargain was shown the identicalproduct by his local merchant for only a dollar acan. Another radio bargain was ten pounds ofprunes for $3.50, of a quality purchasable locallyin one pound packages for twenty-eight cents.HENRYThe Month In RadioOBERMEYER of the ConsolidatedGas Company of New York informsus that his company received morethan 31,000 letters from its customers as a resultof a radio course on homemaking which requiredA TRANSCONTINENTALCANADIAN BROADCASTFor the first time in history, twenty-threeCanadian stations from Halifax to Vancouverwere hooked up in broadcasting the DiamondJubilee Celebrations of the Dominion. A featureof the broadcast was the program ofcarillon music from the Peace Tower in theParliament Buildings at Ottawa (in insert,left). The illustration below shows the controlroom in the Parliament Buildings withtelephones leading to the telegraph and telephoneoffices. Commander C. P. Edwards,head of Canadian radio, is at the extreme rightfour and a half hours of broadcasting time totransmit. One of the important features of thegas company's radio campaign was that anamount equal to fifty per cent, of the broadcastingexpense was spent in newspaper advertisingto call the attention of radio listeners tothe feature. It is an excellent example of successfulcommercial broadcasting which won itsreturn by the real value of its service, I I IThe Bureau of Standards isprepared to calibratecrystal oscillators used in maintaining broadcastingstations on their assigned frequencies, for anominal fee. Stations contemplating taking advantageof this service should first apply to theBureau, giving call letters, assigned frequency,type, make and description of the oscillator tobe calibrated. This information is required becausethe Bureau will not accept for calibrationinstruments which are not so constructed thatthey will remain in adjustment permanently.Ill WHAM, Rochester, New York, whichwill soon have a 5Ooo-watt equipment of thelatest type, WTMJ, Milwaukee and WJAX, Jacksonville,Fla., have been added to one or theother of the N. B. C. chains_,_ giving still greatercoverage to its programs. J I I The NationalElectric Manufacturers' Association recentlycompleted a study of the questionof the number of hours a week the listeneruses his radio set.This information has an importantbearing on the sale of tubes and maintenanceaccessories. According to the NEMAfigures one listener out of a thousand uses hisradio about twenty-two hours out of twentyfour;one out of a hundred, twenty hours out oftwenty-four; one-tenth of the total more thanseven hours a day and four out of five in excessof thirty hours a week, which means five hours anight, six nights out of seven. The statistics wereevidently obtained by making a recordof the listening habits of a handful ofthe most rabid enthusiasts who couldbe found. We would particularly liketo meet the person who uses his radioreceiver twenty-two hours out oftwenty-four. It is quite apparent thatMark Twain was right about statistics.Editor's Note: Mark Twain said:"There are lies, damn lies and statistics."Ill The Canadian radioindustry is developing rapidly. Thereare now at least a dozen first classCanadian-made broadcast receivers,and several factories engaged in themanufacture of radio tubes and batteries.Broadcasting has prospered withthe backing of such powerful concernsas the Canadian National Railwaysand the Northern Electric Company.A patent pool, similar to that of theRadio Corporation of America, islicensing a number of first class manufacturers.On April i, licensed broadcastreceiving stations numbered134,486, as compared with 92,000 atthe end of the previous year. The feescollected from the listener are appliedto the elimination of interference andthe proper administration of commercialradio telegraphy. Ill Danishstatistics inform us that, on April I,1927, there were 130,805 radio receiversin that country, almost equallydivided between crystal and vacuumtube sets, and an increase of 50,000over the previous year. I.i IThere is a great increase in thedemandfor radio receiving sets in Brazil andbroadcast enthusiasm is spreadingthroughout the country with greatrapidity. Most of the stations are

OCTOBER, 1927NEWS OF THE PATENT SITUATION 347along the seaboard and long range receivers secured by John A. Victoreen against the Radio suit resulted in a decision in favor of the latter.are consequently in special demand. American Art Company and others; the latter developed The R. C. A. has already paid $200,000 for rightsreceivers are making the greatest headway in the a substantially different device from that previouslyjudged to infringe. An action was brought unnecessary investment unless they are sustainedunder the Hopkins patents, which will prove anmarket.Federal District Court at Baltimore sustainedTHE Messrs. Willoughby and RADIO Lowell over EQUIPMENT ABOARD THE MORRISSEY IN THE FAR NORTHJamesEdwardRogers in their patent for a submarineManley, of Marietta, Ohio, is shown before the radio apparatus aboard the Putnam-Baffinreception system. Rogers claimed expedition. The Morissey, known to the short-wave code world as VOQ has a generator-poweredprior conception,short-wave transmitter,Willoughby and Lowell clearly anticipatedhim Signals from VOQ have beena battery-powered transmitter using a ux-852 tube (on the top shelf), a shortandlong-wave receiver, and a portable battery-operatedin reduction to practice.clearly heard at the short-wave laboratory of RADIO BROADCAST and occasional radio dispatchesf I f After yielding to a decree pro confesso from the expedition have appeared in the New York TimesLICENSES AND WHAT THEY MEANrequesting that Radio Art be adjudged guilty of before the Supreme Court. * The WestinghouseCompany secured an injunction againstcontempt but, upon submission of a brief that theTHE most important patent decision renderedduring recent months, which is, however, on which the earlier decree had been granted, the Armstrong's radio patent 1,113,149.still subject to future appeal, was that of Judge Court ordered the plaintiff to file a new suit. TheThacher, favorable to the Radio Corporation case is cited in the interests of those who haveTHE COLUMBIA BROADCASTING CHAINagainst E. J. Edmond & Co., Atwater Kent yielded to consent decrees, t t t The ""THE United Independent Broadcasters, ofjobbers. The decision establishes the validity and Eisler Engineering Company of Newark announcesthat it successfully defended itself sports announcer, is a leading official, has given1 which Major J. Andrew White, pioneerscope of the Alexanderson patent 1,173,079, generallyknown as the tuned radio frequency against the General Electric's suit which sought out a list of stations which will form its new network.The key station is WOR, which is the thirdpatent. The result of this decision has been to prevent it from manufacturing tipless tubes.place all concerns making multi-tube sets, not The case was started in October, 1924, and the most popular station in New York, exceededholding R. C. A. licenses in considerable jeopardy.twenty-four important concerns manufacturers, f ? f A suit has been filed The other stations are WEAM and WNAC in Newfinal decision is of interest to all vacuum tube only by WEAF and wjz in number of listeners.have already secured Radio Corporation licenses by the Balsa Wood Company, Inc against the England; WFBL, WMAK, western New York;and those outside the pale are making strenuous Balsa Laboratories Company, Inc. in connection WCAU and WJAS, Pennsylvania; WADC, WAIU,new device was substantially different from that the Kenwood Radio Companyin connection withefforts to secure licenses. So far, no set company with their patent 1,492,982, describing diaphragmsWKRC, Ohio; WCHP, Michigan; WMAQ, Chicago;licenses have been granted which do not guaranteefor sound reproducing devices. It i i and KMOX, St. Louis. Although, in point ofa minimum royalty to the R. C. A. of One claim of V. K. Zwory kin's patent 1,634,390, numbers and station standing, the stations comprising$100,000 a year. Just what the future holds for covering a secrecy system of transmission wasthe chain are not everywhere in the lead,small companies is, at the moment, doubtful. denied because of an earlier patent, Alexanderson's1,426,944. Iff The Brandes Prod-such a chain to corner a good part of the radioit would not take long, given good programs, forRadio dealers are universally demanding apparatuswhich is duly licensed and the position Corporation has petitioned for a writ of audience.of those who cannot, because of small production,guarantee such substantial royalties is Hopkins patent before the Supreme Court. so much as real competition to the N. B. C.certiorari which may bring the dispute regarding Nothing will help the broadcasting situationmost doubtful. The Radio Corporation could not Originally the Lektophone Corporation of Jersey chains, so that both organizations will conductlong withstand the adverse criticism which wouldresult were they to force smaller manufacturersout of business.The object of the patent law is to protect therights of inventors so that they may derive justcompensation for their inventive efforts. The useCity sued the Western Electric Company, which a nip and tuck battle for program supremacy.of patents for restraint of competition, eventhough patents themselves are an intentionaland desirable monopoly, is not supported bypublic opinion. So long as a concern is willingto recognize inventors' rights and pay royaltiesit should not be prevented from engaging incompetitive business. Dealers are justified ininsisting upon licensed apparatus and itappearsthat the Radio Corporation and its licensees arethe only ones who may legally make efficient,high grade radio receivers under present conditions.However, if patents are used in acoercive way to strangle smaller concerns, wedoubt that it will result ultimately to the benefitof the patent holders. No one questions that therecent decisions have established definite supremacyof the R. C. A. in the patent situation,but the advantage should not, and probably willnot, to force be used independents out of business.I if f The Hazeltine Corporation wonCo. sustaining the Hazeltine patents 1,489,228a vitally important decision against A. H. Grebe&and 1,533,858. The distinction between theRice and Hartley disclosures, upon which Grebeplaced principal reliance, and that of Hazeltine,is clearly set forth in the decision. Althoughit isgranted that both Rice and Hartley disclosedprinciples of neutralization, the superiority of theHazeltine method, utilizing a capacity feed backof a voltage to neutralize the regenerative effect,is established as an improvement of great importanceto the radio art. Professor | H. Morecroftappeared as an expert for Grebe The Court,in its opinion, quoted an item from the "Marchof Radio," which Professor Morecroft formerlyprepared for RADIO BROADCAST, acknowledgingthe importance of the Hazeltine disclosure.* I I A decision handed down in the

f I ill -if iC\^the 192By JOHN B.s an Extra R* F* StageBRENNANCascaded Stages Result inSTATIONSSharpness of Tuning but Avoidthe Cutting Off of Side-Bands-ANY discussion centering upon the predominantINrequirements of a modern receiver,it will generally be admitted that there aretwo outstanding things to strive for good qualityand a high degree of selectivity. Strangelyenough, these two coveted qualities are diametricallyopposed to one another difficult of attainmentin the combination.Nowadays, a receiver is judged by its ability tofaithfully reproduce music and speech, and thiscritical attitude on the part of the listener hasresulted in the setting up of a remarkably highstandard so far as the audio channel of the modernreceiver is concerned.The other outstanding requirement,United States has over six-hundred broadcastingstations whereas there were barely a hundredfive years ago.It needs no stretch of the imagination to realizethat there is no receiver which, in a givenlocation, can tune-in all six-hundred of thesestations. With an exceptionally good receiver,however, listeners may tune-in more stationsnot merely the far-distant stations than withjust a fairly good receiver. Yet, in spite of this,there is no advantage gained in such a case unlessthe reception is of good enough quality reproductionto warrant listening to it.To illustrate briefly the difficulties involved,reference to Fig. will iprove helpful. Here asuppositional case ispresented where the verticalrectangular sections represent the ten-kilocyclebands occupied by several stations whose carrierfrequencies are equally separated by a space oftwenty kilocycles. The curve b represents thetuning characteristic of a selective circuit which FIG. Ithat ofselectivity, represents a problem which did notexist in the early days of radio. To-day the^,- Carrier, Frequency-^---- --- - --- ---10 Kc. 10 Kc. 10 Kc. 10 Kc. 10 Kc.FREQUENCYVariable Interstage CouplingProvides for Equal AmplificationThroughout Broadcasting Bandis slightly regenerative and which is set for resonancewith the incoming signal of station B.It will be observed that, while a section of thecurve falls in that part of the space taken up bystations A and C, the amplification of the signalsfrom thest two stations is much below the amplificationof the signalto which the circuit istuned. Maximum amplification of signal A isrepresented by X, the peak of the curve b. Itmay be said of this circuit that it is highly selectivebut it will also be observed that the qualityof the signal isimpaired due to the fact that allthe side-band frequencies, e to f, within the tenkilocycleband of the station to which the circuitis tuned, are not amplified equally. The shadedportion shows how unequal this amplification isand indicates the rapid cutting off of the sidebands. A highly desirable curve would be onewhere equal amplification of all the frequencieswithin the band, e to f, is obtained, and wherethere will be no response obtained to stations inadjacent frequency bands.Now, going to the other extreme, in circuitswherein there is no inherent regeneration, andwhere the characteristic curve indicates broadnessof tuning, as in Fig. 2, it will be noted thatthe shaded portion has become greatly reducedand therefoie practically an equal amplificationof frequencies within the band to which the circuitis tuned, is obtained. It will also be noted,however, that in such a circuit the amplificationof signals obtained from adjacent stations, eventhough the circuit is not tuned to them, is sufficientto cause them being heard as a backgroundto the desired signal. It has been determined thatwhere a number of slightly broadly tuned stagesare arranged in cascade, each successive stagefiltering the output of the preceding stage, and

I1OCTOBER, 1927 THE 1928 "HI-Q" 349.-Carrier Frequency-.production into a practical receiver. It is well known that a three-stage radiofrequencyamplifier can be built to give a high degree of amplification andsmooth operating characteristics; that is, it will have freedom from self oscillation,etc., if it is desired to work at a single wavelength, say, five- hundredmeters. However, where, under these conditions, the circuits are re-tuned to,say, two hundred meters, they will go into violent oscillation and destroythe stability which they formerly possessed. Explained in another way, thismeans that, due to the fact that radio-frequency amplifier circuits have thetendency to oscillate, this oscillation becoming more pronounced as the wavelengthis decreased, a circuit satisfactory for operation at five hundred metersis wholly unsatisfactory for operation at two hundred meters, due to inherentoscillation, unless, of course, some corrective feature, either mechanical orelectrical, is incorporated in the circuit to prevent this oscillation and yetat the same time maintain the circuit at its high degree of amplification.It has been recognized that some system of securing uniform amplificationat all broadcast frequencies is greatly to be desired and various methods forattaining this end have come into prominence during the last year. Thesesystems in the main can be divided into two classes: (i) The mechanicalcontrol of coupling, such as is used in the King "Equamatic," "Hi-Q," andLord systems and, (2) electrical systems, such as those relying on the functionof combinations of capacity, inductance, and resistance the Loftin-Whiteand "Phasatrol" methods, for example.A little calculation will readily show that these systems can be designed toproduce a curve approaching the desired straight line indicating uniformamplification shown in Fig. 4. Since the resultant curve from the use of aFREQUENCYfixed coupling between primary and secondary is so far removed from aFIG. 2straight line characteristic, as will be seen by Fig. 4, even remedial systems,where precautions have been taken to guardagainst inherent regeneration in the severalstages, that the ideal response curve is approximatelyattained. This is graphically shown inFig- 3-From Fig. 2 we have observed that the responsecurve for a single stage is quite broad.It isreproduced again in Fig. 3 as curve No. i.However, when a second tuned stage, having thesame characteristics, is added, the curve obtainedis somewhat altered in form. The top ofthe curve has practically remained the same butits sides have taken a deeper slope, as shown bycurve No. 2. In adding a third stage, the curveobtained is similar to the curve No. 3, whereinthere is a further constriction of the sides of thecurve. The fourth stage confines the curve withinlimits which very nearly approach the ideal.For those who desire a highly technical discussionon the points just outlined, it is recommendedthat reference be made to Professor L. A.Hazeltine's paper on the subject, which is containedin the June, 1926, issue of the Proceedingsof The Institute of Radio Engineers.these principal featuresof a high degree of selectivity and a high degree of re-THE IN new Hammarlund The shield walls have been removed for"Hi-Q" Six receiver,photograph sofour tuned stages are that itemployed and the finalmay be clearly seen how all the parts are disposedresponse curve obtained from their use is similarto No. 4 of Fig. 3. In order to secure this result it was necessary to takeprecautions in setting up the four tuned stages to prevent the desired signalbeing received by any other way than through the antenna into the firsttuned stage, and so on, up to the detector stage. Therefore, the necessity forcompletely shielding each of the stages arose. Also, each of the several tunedstages had to be completely filtered by the use of radio-frequency chokesand bypass condensers so that there were not present any intercoupling effectswhich would cause unstableness in operation and thereby defeat the purposeof the use of these several stages. Were not the radio-frequency currentsconfined to their own individual stages by means of chokes and bypass condensers,and also by the individual stage shields, intercoupling effects wouldundoubtedly be caused either by capacitative coupling from the wiring of thecircuits, inductive coupling between the coils of the various tuned circuits, orresistance coupling in the batteries, since one set of batteries isemployedto furnish the B potential and its impedanceis common to all the tubes.It was realized that all this must be achieved without sacrificing the sensitivityof the circuits, or in other words, their ability to bring in weak signals.This means that the various interstage transformers employed in thetuned circuits must be efficient enough so that weak antenna signals are builtup to a strength sufficient to give a good response in the loud speaker consideringthat two stages of audio-frequency amplification are employed.It is this desire for sensitivity that complicates the problem of combining10 Kc. 10 Kc

350 RADIO BROADCAST OCTOBER, 1927though not absolutely perfect, are undoubtedlya step in the right direction.In the Hammarlund "Hi-Q" Six the resultsobtained by the use of four well designed tunedstages depended not only upon complete isolationof each of the four stages by means of shieldingbut by a combination of mechanical and electricalsystems which, in the end, produced as nearas possible the desired straight line of amplification.The mechanical feature consisted of automaticallyvarying the coupling between theseveral primary and secondary coils by meansof a cam located on the shaft of the condensers,so that a variable degree of coupling was obtainedto give an equal transfer of energy between primaryand secondary regardless of whether thecircuits were tuned to two hundred or fivehundred meters. By the use of the cam methodit is possible to secure the correct degree ofcoupling at any dial setting due to the fact thatthe shape of the cam can be predetermined toprovide the desired coupling. Since all precautionsare taken to prevent feedback by isolatingthe several tuned stages, through the use ofradio-frequency chokes, bypass condensers, andindividual stage shields, only the tube capacityof the tubes employed inthese stages remains tocause undesired coupling.The electrical meansreferred to above is obtainedby the use of "grid"suppressors"r e s i s -tance units located inthe grid circuits of thesetubes. These grid "suppressors"will cancel themUncontrollableFixedPrimaryCouplingtendency of the tube capacityto act as a couplingagent and to causefeed-back.From the detector grid 200to the loud speaker is afixed circuit with constantaudio amplification.The volume control, situated in the radiofrequencyamplifier circuit, permits regulation ofits overall amplification so that the correctamount of signal can be fed to the detector gridto produce a volume of signal from the loudspeaker which is satisfactory t6 the listener. Thecontrol, a filament rheostat which regulates thevoltage applied to the first three radio-frequencyamplifier tube filaments, prevents the overloadingof the detector, especially during receptionfrom powerful local stations. Two stages of audioCIRCUIT DIAGRAM-Equally Good on AllWavelengths-^VWAVELENGTHFIG. 4READY FOR THE BATTERIESThis illustration clearly shows the gauged condenser arrangement employed in the new "Hi-Q" SixVariablePrimaryCouplingV600new "Hi-Q" Six receiver, it will be noted thatdirectly behind the panel there are two metalboxes located at either end, between which is acentral space in which is located the drum dialscontrolling the several tuning condensers. Theleft-hand box shield is divided into two compartmentshousing the first and second radiofrequencyamplifier stages with their associatedchokes and bypass condensers. In the right-handbox shield, also divided by means of a centralwall, are located the third radio-frequency amplifierand the detector stages. The two tuningcondensers in each of these box shields are locatedon common shafts which terminate atthe central space in the drum dials. These dialsarc insulated from the shafts by means of insulatedcoupling units. The following parts areused in building the "Hi-Q" Six:Samson Symphonic Transformerfrequency amplification are employed, good toneof signals being maintained by the use of highqualityaudio-frequencyperfect amplification itvantageous results to be obtained byexpensive$10.00i Samson Type HW-A} Transformertransformers. To secure(3-1 Ratio)necessary that the ad-4 Hammarlund o.oooj-Mfd. Midline5.00the use ofCondenserstransformers be not offset by the un-4 Hammarlund "Hi-Q" Six Auto-Couple Coils4 Hammarlund Type RFC-Sj Radio-Frequency Chokes8.00of tube shouldi Hammarlund Illuminated Drumwith the correct B and C batteries.Dial6.00From theintelligent use of tubes in the audio amplifier.In the last or power audio stage either a ux-i 12(cx-i 12) or ux-iyi (cx-3yi) typebe employedTHE HI-Q SIX-ClOSj B45*B *2nd. Del. 90 157A. F. &R.F. V. V-iSangamo o.ooo25~Mfd. Mica FixedCondenseriSangamo o.ooi-Mfd. Mica FixedCondenseri Pr. of Sangamo Grid Leak Clipsi Carter IR-6 "Imp" Rheostat, 6Ohmsi"Imp"DurhamBatteryMetallized Resistor, 2Megohms3 Parvolt o.5~Mfd. Series A Condenser6 Benjamin No. 9040 Sockets .3 Eby Engraved Binding Posts2 Amperites No. i-AAmperite No. 112iNo. 660 Cable ConnectorYaxleyand Cablei Hammarlund-Roberts "Hi-Q" SixFoundation Unit (containingdrilled and engraved WestinghouseBakelite Micarta panel,completely finished Van Doomsteel chassis, four complete heavyaluminum shields extensionshafts, screws, cams, rocker arms,wire, nuts and all special hardware,required to complete receiver)Total.40.50.101. 0075.503.004.50452.2OI.1O3.0O

The wor\ of the artist and interior decorator as well asthe labors of the radio engineer are evident in 1927-28radio receivers. This Splitdorf "Abbey" set, designed byT^oel S. Dunbdr after an o/d-u;or/d jewel case is a six-tubereceiver, priced at $100. This page and those which followstrikingly demonstrate how the manufacturer is successfullyharmonizing technical receiver design with the decorativedemands of the home. Modern receivers are not one-year in'vestments because the receiver bought to-day will be up-todatefor some time to come; for this, the engineer is responsibleand in later issues of this magazine we shall reportmuch of his fascinating wor\.

352OCTOBER, 19277yZO l\aaio r\eceiuersFRESHMAN G-4Here is a new electricallyoperated Freshman receiver,complete and ready tooperate as delivered. Theprice is $225.00, which includesnew RCA a. c. tubesOFTEN it is said that a radio receiver, to be fully appreciatedby the feminine half of the domestic republic, must be encasedin housings which are esthetically as well as technically satisfactory.It is natural and right that, as radio has becomemore an accepted part of the equipment of every home,women have had an increasing voice in the selectionof the radio receiver. What, then, do the radiomanufacturers offer to the prospective purchaser?To be brief, the radio receiver of1927-28 is a thing of beauty as well as ofutility. On these two pages, and onothers in this issue, are grouped illustrationsof the sets which havecome from the manufacturers'STEWART-designing laboratories. Variousmakers have grappledwith the important problemof appearance,and, as these illus-THEWARNER 520The tendency towardssingle-controlis again manifest inthis six- lube receiver. Two tunedand one untunedstages of r. f.,detector, and twotransformer-coupledaudio stages, comprisethe circuit.The cabinet is ofdull polished walnutveneer. The price,$125.00show,trationshave met itinwidelydifferentBOSCH 66Another single-controlreceiver employing sixtubes, this one beingpriced under a hundreddollars. The beauty ofthe cabinet is a featurebut the efficiency of tbecircuit itself has in noway been neglected.The illuminated dial isgraduated into bothkilocycles and arbitrarynumbersGREBE'S "SYNCHROPHASE" SEVENThe five tuned stapes (four r. f. and detector) aretuned by means of a single dial and vernier, therigidity of the tuning condenser assembly insuring]>ermanency of the accurate factory ucl j tistment. Thereceiver has been carefully shielded, while the specialcoils employed enhance the selectivity and permitmaximum amplification. These coils are of thebinocular type and are wound with Litz wireThis is a six-tube, non oscillating,t. r. f. set, balanced and shielded."Inductance tuning" is employed,a system which requires no variablecondensers and which permits equalamplification throughout the frequencyspectrum covered. The priceof the receiver is $190.00"COMMANDER"Here is a King sixtubecompletelyshielded t. r. f. receiverwhich makesuse of single controltuning. There arethree r. f. stages.The loop may befolded into the cabinet.Price $220.00

hoyOCTOBER, 1927 353ofneaviiy and CiuUn/ways. Some of these models achieve their decorative effect throughthe dignity of utter simplicity; others are notable for the use ofornament in the treatment of the control elements. The metaltuning and control escutcheon is supplied with somedecoration, slightly reminiscent of that simplicity to befound in the grouping of instruments on present dayautomobile dashboards. Illumination of the controlescutcheon is also a feature which has much incommon with the instrument panel on themodern motorcar. From the representativemodels shown on these pages, the housewifecan gain an excellent idea of theappearance of moderate priced radioreceivers which are offered tosuit her taste as well as thatof her husband. Herideasofthe necessary limitationsof her domestic decorativescheme shouldb le n d withher husband'stechnicalopinions.WORKRITEThis eight-tube receiver hasall-metal chassis, and completecopper shielding.There is a single illuminateddrum type dial control.Price, $160.00 without tableBELOWThe Kolster 6H consists of asix-tube receiver power conereproducer, and B socket powerunit. Space is provided foreither an A socket power deviceor a storage battery,which is extra. Price, $265.00THE "WARWICK"In a cabinet of Tudor period. A sixtubeSpUtdorf receiver, similar tothat shown on page 351. is built in.Price, $275.00 with cone andpower-supply unitZENITHThe Model 17E electric.A single-tube 400-mA. unit supplies thenecessary power. Thereceiver itself employssix tubes. The price is$350.00. Spinet base,$20.00 extraTHE "NAVAJO"Six tubes, shielded,-single controlthese words describethis new Mohawkreceiver justMS I do otherprominent receiversof the season, forlliis circuit combinationpn'

354 RADIO BROADCAST OCTOBER, 1927THE 'BANDBOX'*This is a recent presentation of the CrosleyCorporation. It is a six-tube neutrodynemade in two models, for battery or lump-shielded, and has one-socket operation, isdial tuning. The prices are $55 and $65, forbattery and a. c. operation respectivelyTheNeutrodyneGroupA LOOP NEUTRODYNEIt is a Freed-Eisemann eighttubesingle-control receiver,retailing for $395.00 with acone loud speaker, as illustratedTHE RADIO-PHONOGRAPHThis Stromberg-Carlson masterpiececonsists of a completea. c. operated seven-lube singletuning control receiver combinedwith a modern electric phonograph.A concealed loop obviatesthe use of outdoor antenna.Price is $1245 completelyequipped with cone loud speaker

OCTOBER, 1927 THE NEUTRODYNE GROUP 355FA DAThree r. f. Hinges, two tuningcontrols, one-niece steelchassis, aud equalized amplification,are features ofthe Fada "Special," retailing at $93.00f II 1O THE lay radio reader the term "Neutrodyne"means a type of receiver only a|" well-known type of long standing merit.To the engineer the term signifies much more. Itrecalls the researches of Professor Louis Hazeltineof Stevens Institute of Technology; it bringsthe patent office to his mind; it indicates one ofthe present group of radio set manufacturers whohave availed themselves of Professor Hazeltine'sinventions.For four years, the neutrodyne group, now consistingof Amrad, Fada, Freed-Eisemann, Crosley,Murdock, Workrite, Gilfillan, Howard,Garod, and Stromberg-Carlson have built receiversthat were representative of the best workof the best engineers. These receivers have becomeknown for their reliability, their sensitivity,simplicity, and generally excellent service. Theyneed no introduction to the American radiopublic. Of late, those who read the foreign radiopress have noted the large number of times theFrench, English, Spanish, and German papershave described the neutrodyne, indicating thatFOR THE "BANDBOX"This console has been speciallydesigned for the Crosley "Bandbox,"illustrated on the left-handpage. The "Bandbox." the chassisof which is completely shielded,may quickly be removed from itsmetal cabinet and inserted in themore pretentious consoleTHE FADA 7It is optional whether loopor antenna i.s used with thisreceiver, which has fourstages of r. f. An improvementin the detector circuitreduces the possibilities ofoverloading. This seventubereceiver sells for $185.00Europe is following advances in American radiowith great interest.For the coming radio season, the neutrodynegroup has been more than busy, as the accompanyingphotographs will show. In common withother well organized receiver manufacturers, thegroup has spent money and time in research forbetter radio components, for even greater simplicityof operation, and for greater fidelity ofreproduction. A glance will show cabinet workthat cannot help but amuse those who rememberthe early days of radio, when a conglomerationof wires and roughly assembled apparatus, frequentlyboasting no kind of housing whatever,was principally useful in collecting dust.AMR AD'S "THE WINDSOR"This artistic cabinet houses a very efficient seven-tube neutrodyne chassis. Tuningis accomplished by a single dial and a further adjustment is provided for volumecontrol. Either an antenna or loop may be used and all parts are copper shielded.A tone tiller is incorporated. The price is $195

356RADIO BROADCAST OCTOBER, 1927A MARTI RECEIVERTHE "MAYFLOWER"a. c.Here is a five-tube completelyoperated receiver by Cleartone, ofCincinnati. Complete with a. c. tubes,loud speaker, and built-in power unit,Another electric receiver,this one employing sixtubes, three of which constitutethe audio channel,resistance coupling beingfeatured. Tuning is accomplishedby means of twodialsewamror^^ UOUT&& J ** * ^^^^iThe Radio Receiver Powered Directly fromthe Light Socket is like the Automobile withPushing the Button Starts theMachinea Self-StarterModels on This Page are Representativeof the Season's A. C. Set Offerings.TO THE LEFTThe well-known Lnftin-White circuit,s x tubes, is employed in the ArborloneModel 253 receiver. Tuning isI,Tomplishccl by means of a single dialilibrated in wavelengths. A Peerlessme loud speaker is included, and theceiver may he used with either bateriesor socket-power devices. Thecabinet is of matched walnut, curlymaple and rosewood veneers, and gumwood.Price. $250.00A NEW DEPARTURE IN POWERSUPPLYThe Day-Fan Electric Company, ofDayton, Ohio, has placed on the marketreceivers which are powered by motorgenerators, all batteries being eliminated.The efficiency of the motorgenerator principle of ^transformingalternating current to direct currenthas long been recognized, but its applicationt the powering of a radioreceiver has hitherto been neglected,so far as receivers commercially availableare concernedAN ECONOMICAL A. C. RECEIVERThe manufacturers of this receiver, theArgus Radio Corporation, of New YorkCity, state that the cost of operating thisreceiver is no more than one fifth of a centper hour. The receiver is completely a. c.Operated, and employs 110 batteries orchargers. There are six tubes in all. three ofwhich are r. f . in a combination of tuned anduntuned stages. The final audio stage employsa 210 type tube, a plate potential of400 volts being applied to it. Provision ismade so that the audio amplifier may beused in conjunction with a phonographpick-up device. Price $195.00, less tubes andloud speaker

OCTOBER, 1927 SERVANTS OF YOUR LIGHT SOCKET 357LEFTThis is a Freed -Eisemann electricallyoperated receiver,listing at$295.00. A neutrodynecircuit is used,and extraordinaryselectivity is claimedby the manufacturersAN ALL-AMERICAN HIBOYThe receiver employs six tubes, and maybe obtained either to use the new a. c.tubes or for ordinary tubes, batteries orpower unite being required in the lattercaseSPARTON MODEL 62Everything, with the exceptionof the loud speaker,is self-contained in this newelectee receiver by Sparks-Withington. No batteriesare required. The price,$188.00BUCKINGHAMHere is a receiver whichmay be used with eitherbatteries or power units.It employs six tubes, threeof which are r. f. stages. Thesingle-dial control systememployed is a special Buckinghampatent. The dial isilluminated and calibratedin both kilocycles and degreesTHE CASE CONSOLEAn enclosed .oop, controlled from the front panel, obviatesthe necessity for an outdoor antenna. The receiver employsnine tubes and tuning is accomplished by means of a singledial. It is equipped with a Newcombe-Hawley loud speaker,which has an air column of seventy-two inches. The price ofthe console is $350.00, less accessories. The receiver is alsoobtainable for use with a. c. tubes, in which case the listprice is $475.00 complete with tubes and ready to operateTO THE LEFTThe electric receiver drawer of McMillan. Chicago. This drawer forms the nucleus of several attractivereceivers by McMillan, ranging in price from $260.00 to $325.00. A table cabinet model lists at $170.00ELKAY "SENIOR"Complete a. c. operalionwith every necessarypiece of equipmentbuilt in, unified tuningcontrol, "Truphouicaudio amplification, toalcopper shielding, sixulx^s thus can thislew Elkay receiver belescribed. The list prices $195.00. Six McCullougha. c. tubes, andone Raytheon BH rectifier,are required asextras

THE NEW RADIOLA 17A receiver which makes use of the newa. c. tubes in the first five stages and a171 type tube in the final (second) audiostage. The receiver may therefore besupplied with A jtowerfrom the houselighting circuit without the use of additionalequipment. B and C batteriesare also eliminated by the useof a suitablepower device which is built in.Price $130.00A NEW CONEThe new 100-A coneloud speaker pricedat $35.00A CUSTOM-HUILT RADIO RECEIVERThe Radiola 32 combines the well-known RCA eight-tube super-heterodyne and abaflleboard loud speaker in a single cabinet. Since a loop, directionally variable, isbuilt in this receiver, it may be used where facilities for outdoor antenna erectionare not available although binding posts are provided for antenna and ground ifsuch are used. All current is obtained by plugging into the house lighting supply.The model is obtainable for either a. c. or d. c. operation. Price $895.00 complete? If 'HE super-heterodyne and the tuned radio-frequency circuit,with or without regenerative action, continue as the foundations^ of the 1927-28 line of receivers offered by the Radio Corporationof America. A parchment cone, with properly balanced drive forthe moderate power of the battery set or again the high power of thesocket-power set, likewise continues as the basis of the Radiola loudspeaker offerings. Alternating-current operation, with certain refinementsparticularly by way of rectifier tubes of increased output andbetter voltage regulation, makes a bid for favor in the higher pricedcombinations. The Radio Corporation has also added the new a. c.tubes as a means of electrifying even the moderate-priced Radiolas,the ux-227 heater type for the detector socket and the rugged filamentux-226 for all other positions.Starting out with the requirements of the modest home, there is thenew Radiola 16, which fulfills the most rigid requirements of sensitivity,selectivity, ample volume, simplified operation, and excellenttone quality when used in combination with the new Radiola loo-Aloud speaker. The Radiola 16 isa new uni-control six-tube receiver,embodying the well-known and perfected tuned radio-frequencycircuit with three stages of radio-frequency amplification, a detector,and two stages of audio-frequency amplification, and utilizing fiveux-aoi-A and one ux-112 tubes. The power tube in the last stagespells ample volume without possibility of distortion due to overloading.The internal construction of this Radiola is extremely rugged.The operation is reduced to one tuning control which can be loggedfor the station call letters. There is also a volume control, and a filamentswitch which starts and stops the reception of programs. Tosimplify the operation still further, the filament rheostats have beendispensed with. Radiola 16 may be operated from batteries or from asocket-power device. The cabinet of this receiver is of mahoganyfinish, and measures 165" long, 8j" high, and yj" deep. The weight is145 pounds, and the price, $69.50 less accessories.Next comes the Radiola 17, aimed to produce, fora moderate price,a receiver completely operated from the a. c. house lighting mains.Simplicity of operation and maintenance are the main features ofRadiola 17. It has three stages of radio-frequency amplification, adetector, and two stages of audio-frequency amplification. The newux-226 a. c. tubes are used in the radio-frequency stages and in thefirst audio-frequency stage, while the new uv-22- a. c. tube is used asa detector. The last audio-frequency stage employs 3171 power tube.The B and C voltages are obtained from a power supply unit built intothe set and employing the new high-power ux-28o full-wave rectifier.There are only three controls on this set, one knob for tuning, onefor volume control to regulate the output of the receiver, and apower control switch to turn the receiver on or off.Inside this new Radiola 17 is located a switch whereby adjustmentmay be made for any variation in local line voltages between 105 to125 volts. The size of the mahogany cabinet is 25^" long, jl"deep, and 8|" high. The receiver weighs 36^ pounds, and retails for$ 130.00 without accessories.The well-known Radiola 20, with its two stages of radio-frequencyamplification, its regenerative detector, and two stages of audiofrequency, employing the economical ux-igg and ux-120 dry-cell

UKSIX TUBES AND SINGLECONTROLThe new $69.50 Hadiola 16. This receiver,like the 17 illustrated atop theprevious page, also employs three r. f.stages, detector, and two transformercoupledaudio stages, but the tubes arenot of the a. c. type. The output audiotube is of the 112 type as opposed to the171 in the Radiola 17. Tuning is accomplishedby means of a single controlknob, but there are also a volume-controlknob and a filament switchtubes, continues to occupy its place in the RCA line. This Radiola hasproved a popular favorite, and for that reason it has been retainedamong the present offerings. It now lists for $78.00 less accessories.Likewise with Radiola 26, the six-tube portable super-heterodynewith its self-contained loop, loud speaker, and dry batteries, which hasprovided vacationists and travelers with satisfactory and convenientradio service, and which retails at 1225.00 complete. Radiola 25, asix-tube super-heterodyne priced at $165.00 with tubes, is also beingretained for 1928 offering.Turning to the higher-priced offerings, there remain the well-knownRadiola 28, or eight-tube super-heterodyne, and the Radiola 104 loudspeaker, which, in combination, provide an exceptionally sensitiveset which may be completely powered from the a. c. house lightingTHE RADIOLA 20This is not a new season's model but it has been carried over on accountof its popularity. It is a flve-tube t. r. f. receiver with knurled-dial tuning.Its price is $78.00 and it may readily be adapted for a. c. operationsystem. The price of the Radiola 28 is $260.00 with tubes. The 104loud speaker units cost $275.00 or 1310.00, for a.c. or d.c. operationrespectively. Radiola 32, a newcomer to the Radio Corporation's line,with its handsome walnut grained cabinet in period design, consists ofan eight-tube super-heterodyne, loop, Radiola 104 loud speaker, and isoperated from the house lighting system. It provides maximum radioresults in the most compact and attractive form. Certain refinementsin design have permitted the inclusion of the powerful 104 loudspeaker actually in the same cabinet as the super-heterodyne. The new32 receiver has a self-contained loop which is turned by means of aknurled dial mounted near the loud speaker grille. Another featureis the small electric light bulb which is concealed in the top of theoperating compartment to illuminate the dials and also to serve as awarning indicator when the current is turned on. The poweris automaticallyswitched off when the set is closed. The cabinet measures52" high, 72" wide, and 17!" deep. The list price is 895.00, which isinclusive of all accessories.A somewhat lower-priced model, but likewise characterized by adistinctive cabinet and entirely self-contained equipment, is theRadiola 3O-A, comprising the eight-tube super-heterodyne with thenew loo-A loud speaker and an arrangement whereby the set may bepowered from the house lighting supply. The Radiola 3O-A measures42^" high, 29" wide, and 17!" and its deep, list price is $495.00,including all the necessary accessories. Unlike the more expensiveRadiola 32, no loop is contained in the cabinet of the 3O-A, antennaand ground connections being provided on the rear. A short indoorantenna is recommended for use with this receiver.Both of the latter, Radiolas, 32 and 3O-A, may be had for alternatingcurrent or direct-current operation. Furthermore, the 104 loud speakerunit is now available in a direct-current model, as mentioned above.The new Radiola loo-A loud speaker referred to above is the improvedloud speaker for use with all receivers, whether they areoperating on batteries or with socket-power equipment. The coneitself is of smaller diameter than the well-known 100 type, which itreplaces and, in addition, embodies a newly designed drive that providesincreased response with even better tone quality than its predecessor.The cone is enclosed in an attractive metal case, suggestive ofa mantelpiece clock, with silk screen bezel, the whole being finished indull bronze. This new cone loud speaker measures approximately 15"x n" and retails for ^35.RADIOLA 30-AThe .-ircuit employed in this new receiver is identically the same as that of the"Kudiola" 36, i. e., an eight-tube super-heterodyne and it is operated from thelight socket. The 30-A retails for considerably less than the 32, however, its listprice being $495.00 complete. The differentiating features of the less expensivemodel are: (1) The 100-A cone is employed instead of the more powerful and moreexpensive bailleboard loud speaker, and (2) no loop is supplied. Antenna and groundconnections are provided, and for average reception an ordinary indoor antenna willbe satisfactory

360OCTOBER, 1927FOR B AND C VOLTAGESGrebe offers an attractive socket power unit for radio receivingsets of from five to seven tubes. There are three B taps, 180, 90,and 22 volts, and two C values, 40 and 4 volts. Special designfeatures have been applied to obviate "motor boating"A POWER CONE REPRODUCERIn addition to the cone loud speaker, this Kolster power assembly comprisesa B power device to furnish the necessary voltages to operate any commercialreceiver. It is operated from the 60-cycle 110-volt a. c. house supplyThe price is $150.00 without tubes. Two rectifier tubes (CX-316-B orUX-216-B), a regulator tube, and a power tube (CX-310 or UX-210). arenecessaryLond Speakers, Cabinets andAccessories offered by VarioiisMakers Show Definite NewTrendsVALLEYTONE MODEL 52A Gve-tube receiver to suit the average pocket, its listprice being $85.00, less accessories. Tuning is accomplishedby means of two dials. A simple switching arrangementbuilt into the set makes the use of a powertube optionalLEFTThe " Spinet," a seventubebalanced receiverby Colin B. Kennedy,Incorporated. There arefour r. f. stages but justOIK- tuning control. Thelinish is of two-toneantique mahogany, andthere is ample storagespace for power accescessories.Price, $195.00FOR THE SET CONSTRUCTORKeeping apace with the commercial set manufacturer, the home constructorof the Radio Master Corporation, Bay City, Michigan

OCTOBER, 1927 361THE BOSCH "NOBATTRY"This attractive unit is designed to tlcliver three B voltages, thetaps being labelled ''low." "medium," and "high." The listpries of the device is $ 18.00. Taps on the transformer providefor three separate voltage rangesAll, while Serviceable and of InterestingTechnical Design Are Madeto Harmonize with Their Eventualthe Home.SettingTHE "MINSTREL"A successful antenna operated receiver is this seven-tube, single-control.Apex set. The circuit employed is of the " Technidyne" variety, one that hasbecome increasingly popular lately, and which makes use of a new form ofneutralization. Less accessories, the "Minstrel" lists for $225.00ABOVEThis is the Pfanstiehl Model 30six-tube receiver. Its chassis iscarefully shielded and equippedwith flexible cable connections.Price, $105.00RIGHTThe "Baby Grand," byAudiola, Chicago, comeswith either an eight-tube orsix-tube chassis, the formerlisting at $275.00 and thelatter at $225.00. There aretwo knobs on each model,one for tuning, and thesecond for volume control.Individual stage shieldingadds to the general efliciencyof the set. A .-pecinllong air-column loudspeaker is built inDESIGNED FOH A RADIO SETHere is another example of the cabinet makers' efforts to produce a radiocabinet which is in every respect equally as beautiful as the furniture surrounding!t. The finish of this particular cabinet is in walnut andand mapleit is equipped with a Farrand cone loud speaker. 1 1 is designed to accommodateall standard makes of radio receivers, and is a product of the M usicalProducts Distributing Company, New York City. Price $95 00

362 OCTOBER, 1927B POWERThe Kellogg B powerunit has the usualthree taps, for defector," "medium,"and "high," but additional flexibility isobtainable by means of the knobs onthe front panel. The detector voltagemay be adjusted to any value up to 45,while the medium voltage tap may beset for anything up to 90 volts. Thehigh-voltage tap is for a 171 type tube.Forty dollars is the price of the unitAN ELLIPTICAL CONEThe frame and base of this new Splitdorf cone is of richantique walnut finish, deeply carved, the result, being aloud speaker which will enhance almost any setting. Theelliptical shape of the cone makes possible deep richlyresonant tones, the short diameter of the ellipse favoringthe high notes, and the long diameter sustaining thedeep tones. A combination of design features enablesthe loud speaker to handle great power. The list price is$35.00AN AUTOMATIC CHARGERA charging unit developed by the Westinghpuse Companyiisincorporated m this useful Apco device. Full-waverectification is accomplished by means of a series of specialanalysis copper discs in the transformer circuit. An automaticrelay is combined with the Westinghouse unit so that,-once connected to the set, the charger is spontaneously setin operation when the receiver is not being used. The listprice of this Apco unit is $16.50A UNIT THAT SUPPLIES BOTH A AND B CURRENTUnlike many other units designed to supply both A and B current, this one does not use a storage batteryin conjunction with a trickle charger. A rectifier and electrolytic filter condenser, combined in one cell,constitute the A unit. There are no tubes to burn out, the only attention necessary being the additionof water every three or four months. This Halktte "AB" is obtainable in two patterns, both with anoutput of 6 volts, 2 amperes, for the A supply, but one has a B output of 40 mA., 135 volts, while thesecond gives 55 mA., 180 volts. The prices are $59.50 and $67.50 respectivelyA AND B POWER FROM ONE UNITAcme, of Cleveland, is responsible for this useful power combination.Included in the unit is a B socket-power device, a 40ampere-hour storage battery, trickle charger, and automaticcontrol switch. The unit may be obtained for 25- or 60-cycleliouse supply, and for sets with varying amounts of tubes, theprices being between $95.00 and $108.50THREE LOUD SPEAKERS IN DISGUISEThe group of books, in the first place, is nothing less than a loud inspeakerconcealment. A forty-inchserpentine tone chamber winds behind the embossed leather book bindings. This " Choral Cabinet" listsat $50.00, or $75.00 if the equestrienne bronzes are included. The lamp too, in addition to serving itsobvious purpose, hides an air-column loud speaker. Depending upon the finish, it lists at $35, $50.00,or $60.00. The carved picture frame to the left also conceals a loud speaker, the tone chamber of whichis a thirty-inch serpentine winding. The hand carved black walnut model lists at $35.00, but othermodels are less expensive even as low as $20.00. Manufactured by Frank R. Porter, Washington,District of Columbia

Why It Is Desirable to Employ aRegulator Tube in B Devices De-THE voltage-regulator tube received itsrather descriptive nickname, "glow tube,"from the performance of some of the earlymodels which, having an open top cathode, permittedan observer to see the ionized gas or"glow" in the space between the anode and cathode.This tube is a device which, when connectedacross the go-volt output of a B power-supplyunit, will maintain that voltage at a constantvalue, regardless of any variations in load,within reasonable limits, applied to the powerunit. Without the use of such a regulator, thevoltage supplied by the device will fall off rapidlyas the current drain is increased.By using a regulator tube, it is possible toconstruct a B power unit, the go-volt tap ofwhich will, for all practical purposes, delivervoltage across the operating electrodes at anyjust 90 volts to any radio receiver whether ittime fall below the valueRADIO BROADCASThas 3 or 10 tubes. In the case of the Photographrequired to maintainmajoritytheINNER CONSTRUCTIONgas in an ionized state, the potential of theof radio receivers the go-volt tap supplies thethird element will be sufficient to maintainBThe bulb has been removed to showpower for the radio-frequency and first audioionization. In order to minimize the extra drainstages. In the case of a the electrodes of the "R" tubesuper-heterodyne, howon the rectifier and filter, a forty-thousand ohmever, the go-volt tap will also have to supplyresistor isemployedthe B power for the intermediate-frequencyBy JAMES MILLENto limit this parasitic currentto approximately three milliamperes.amplifier. Incidentally, as the load drawn by theAs a result of the third element and its associated"keep alive" circuit, the high startingdetector tube, in most sets, is substantially thesame, a suitable resistor with mid-tap may be lower voltage and thus less expensive bypass voltage required by former types of regulatorconnected across the voltage regulator tube condensers at the various voltage taps.tubes is eliminated.terminals to provide a fixed 45-volt tap. Now, The itfirst type of voltage regulator tube to The base contacts on the new "R" tube, asalso happens that, when the regulator tube is appear on the market was of the two-element it has been named by the manufacturers, theused, variations in load on the 90- and 45-volt type and, like the prototype of most things, had Raytheon Company, are so arranged as to permitits use in B units and combinationtaps will have no effect upon the maximum its disadvantages. Different tubes varied considerablyin characteristics, some having a amplifier B units designed originally for the ux-voltage tap of the power unit. The powervoltage at thispoint will, however, vary with the load at the working voltage of as low as 70, while others had 874 (cx-374) the original voltage regulatorhigh-voltage tap; but as we know that the usual over 100. Then, the voltage across individual tube placed on the market. When so used, theload to be applied to the high-voltage tapis a tubes would vary quite a bit between conditions third element does not operate.ux-171 or cx-371 type power tube, and that at of no load and full load. Another fault was that, While the tube may be added, along with suitableresistors, to some of the heavy-duty type180 volts this tube will draw a plate current of should the power unit be heavily loaded for any20 mA., we can so design our power unit to reason, the tube would cease to glow and, before B power units now on the market which havesupply exactly 20 mA. at 180 volts.again becoming operative, the voltage across it not been specially designed for use with a glowThe result is a fixed-voltage power device would have to rise to a rather high value, which tube, it cannot be used with the average runwhich will supply 45, 90, and 180 volts to almost eliminated the possibility of partially providing of socket power-supply units due to the extraany standard radio receiver. Fixed-voltage control,however, is but one of the many points of voltage bypass condensers.chokes. Likewise, in home constructing a powerfor the initial cost of the tube by the use of low-load it imposes upon the rectifier and filtermerit of a "glow-tube" equipped power-supply But perhaps the most serious objection to unit employing the "R" tube, chokes capableunit.former voltage regulator tubes was the tendency of handling at least 85 milliamperes of directThe action of the tube in holding the voltageof many of them to oscillate and introduce noise current without core saturation must be selected.of the output circuit constant serves also to into the output circuit of the power unit. The At this time we are familiar with only twoeliminate the small ripples which may be presentas a result of incomplete filtering, and thus would often introduce sufficient noise into the the National and the Amertran. The rectifieruse of a power unit equipped with such a tube chokes on the market that meet this conditionmakes possible a reduction in the capacity, and loud speaker to interfere with satisfactory reception.But now, after several years of research type. The power transformer should have atube should be of the 85- and not the 6o-mA.therefore the expense, of the final filter condenser.In fact, the tube, when in operation, has and experimental work, a new form ofmany properties in common voltage double high-voltage secondary with a voltagewith a large fixedof 300 across each side.condenser. One of these properties is extremelylow a.c. impedance which, when combined withits instantaneous response as a voltage regulator,entirely eliminates the annoying "motorboating"effect which generally results when anattempt is made to use one of the ordinary Bpower units with many forms of amplifiers.A further advantage accruing from the constructionof a B power unit employing a voltageregulator tube is an economical one. With itsmany electrical advantages, it need cost nomore than that of a high-grade power unit ofthe conventional type. In the first place, theuse of the "glow tube" results in a saving ofOBthenumber of high-voltage filter condensersrequired usually an expensive item. In theA B-DEVICE WITH THE NEW "R" TUBEsecond place, itpermits the use of fewer and The new Raytheon tube has five leads, the fifth connecting to the metal pin in the tube basetails of a New Qlow Tube WhichInvolves Some Novel FeaturesIts small size and low cost permit its readyuse in many cases where the older form of tubewas out of the question. Its silent non-oscillatingoperation, its long life, its close control of voltage(a variation of but 3 volts between a conditionof no load and full load being allowed), andthe use of a third or "keep-alive" element, areall features which make it one of the most interestingdevelopments in the B power-supplyfield since the introduction of the filamentlessfull-wave gaseous conduction rectifiers.glass tube ionized at all times. Thus, should theregulator has been perfected.The "keep alive" circuit is a most unique arrangementof what really amounts to a tubewithin a tube. The inner, or secondary tube,operates without load from a high-voltage pointof the filter circuit and keeps the gas within the

366 RADIO BROADCAST OCTOBER, 1927The builder of this new "Equamatic" receivershould have no difficulty in making aone hundred per cent, workable set at the firsttrial. The parts have been so placed that interactionbetween circuits, which ordinarily is adifficult problem with which to cope, is minimized,and the progressively increasing couplingbetween circuits at the longer wavelengths providesthe proper interstage energy transfer. Thefirst "Equamatic" coil, which transfers energyfrom the antenna circuit to the receiver proper,may be arranged to have a slightly differentrate of change of couplingif desired if the userwishes somewhat greater selectivity for example.In this case, the coupling at the lowest frequencymay be decreased by making the primaryand secondary not parallel, but turned at aslight angle. In general, however, the greatestcoupling should be used at all times, and asomewhat smaller antenna used if greater selectivityis desired.The condensers which tune this receiver, ifthose specified are used, have a straight frequency-linecharacteristic,a decided advantagenow that transmittingstations areagain operating onten-kilocycle separations.If it is desiredto use a 171 typetube, somewhat differentconnections mustbe made to the lasttwo tubes and theirplate circuits. As wiredaccording to Fig. I,RADIO BROADCAST Photographreduction, and theirthe last two tubes getthe same B Here is the voltage,1927 "Equamatic" which now exceptionally smoothis improved. Note the three-dial tuningaction, make tuningthis being necessarya joy. The writeron account of the interstage switch. Additional tor. The condensers, for instance, are new, in found that the receiver tuned with great easeprongs would be necessary if the two audio that they are equipped with removable shafts although it was sharp enough to please a criticalfan.tubes needed different B voltages. In the so that insulated ones may be substituted forvicinity of broadcasting stations, however, the metal ones, and complete insulation from All in all, the home constructor should findthe field strength is sufficient to give all the hand capacity thereby realized. In some circuitsvolume one can desire by using a semi-power this is important; in the present receiver, handtube of the 112 type. At some distance fromstations, the 112 tube with its greater amplifi-Holes No. li2-VD,.;i Holes No. 344- VDrill Hole No. 7 -VCHoles No. 5,6.4 8 - No. 26 Drill 4 Csk. (or 632 Screw1__t _._AjVolume1st SlageDetktor1 Off-Q- 2nd. SI- %J~ 2W- U 6^- **.i*-.*!--" 4-k 24'FRONT PANEL DRILLING INSTRUCTIONScation factor will have an actual advantageover the 171 type, and louder signals will beobtained. Thus weaker stations will operate aloud speaker.Now that we have outlined the electrical featuresof this new " Equamatic" circuit, there areseveral mechanical notes which should bebroughtto the attention of the home construc-capacity will not be apparent owing] to the factthat the rotor plates of the condensers are at-W'l'Wjground potential. The output filter, which is newin this year's model, consists of a conventionalchoke and condenser combination and, as may beseen in an accompanying photograph,is builtinto a round metal box similar to the audio transformers.The latter, incidentally, have exceptionallyhigh primary inductance, which isnecessaryfor full reproduction of low audio frequencies.Their turns ratio isabout 2.5 to i.In all receivers employingtwo or moretuned circuits, tuningis inherently sharp,making necessarysome form of fine adjustment.In this receiverthe designershave used the familiarKaras dials which,with their 63 to ithis receiver a well designed, simple-to-construct,high-quality set, and in building one, hewill be equipping himself with a receiver ofwhich he can be deservedly proud.RADIO BROADCAST PhotographLOOKING DOWN ON THE 1928 "EQUAMATIC"The arrangement of parts is neat and efficient. Note the lever pantograph arrangementwhich makes possible simultaneous adjustment of the second and third tuned circuits

A New PrincipleR TutiitiiThe "Octa-Monic" System Resonates the Second Harmonic Insteadof the More Usual FundamentalBy DAVID GRIMESIncreasing the SelectivityUP TO the presentjusttime therehave beenthree fundamental radio circuits,and every type of radio receiver has employedsome variation of these three arrangements.First, there was the regenerative system;next radio-frequency amplification was developed;and last, the War and Major Armstrongproduced the super-heterodyne.Regeneration is a principle by which increasedsignals may be obtained by a properly phasedfeed-back or reenforcement of the incomingsignals. When radio broadcasting first becamepopular in 1922, the regenerative type of circuitwas generally used. The feed-back action madethe receiver very sensitive for distant receptionand very selective at the particular frequencyfor which the receiver was tuned. As the numberof stations increased, and two or more powerfullocal stations became established in manycommunities, the regenerative receiver ceasedto give satisfaction because of its broadness oftuning. Near-by locals could not, therefore, betuned out. The necessity for extra selectivity wasmet by sets with tuned radio-frequency amplification.But the standard two-stage tuned radiofrequencysets soon became inadequate becauseinherent resistances in the vacuum tubes andassociated circuits limited the ultimate selectivityto be obtained therefrom. Attempts to offsetthese resistances by feed-back circuitshave been somewhat successful in increasing theselectivity but in nearly every case the audioquality has suffered. The RGS Inverse Duplex,described in the January, February, and March,1927 issues of RADIO BROADCAST, employed atuned radio-frequency circuit with an automaticnegative resistance circuit which greatly increasedthe selectivity at all wavelengths. Thelimiting factor was the tone quality, however, assuper-selectivity tends to cut the side-bands on acarrier wave, thus sacrificing the high pitchaudio tones. The selectivity of the RGS InverseDuplex was carried to such a point that a specialaudio circuit was employed to give extra amplificationto the high-pitched tones in an effortto provide for the reduction in side-bands.The super-heterodyne came into general usemainly because of its selective properties and itsextreme sensitivity, permitting loop operation.But the side-band limitation so characteristicof a really selective tuned radio-frequency setbecame very noticeable in super-heterodynecircuits employing low-frequency intermediatetransformers. Here the plus and minus jooo-cyclevariation which must pass through to insuregood tone quality is a very large percentage ofthe intermediate carrier wave of 30,000 or 50,000cycles. The resonant curve must therefore bequite broad, which somewhat offsets the veryDAVID GRIMESimpedance exists in the plate circuit. This curvedcharacteristic leads to distortion which is anothername for the generation of harmonics. Inthe plate circuit of the average r. f. amplifier isonly a small impedance, therefore in this circuitexist the second harmonic as well as the fundamentalimage of what occurs in the grid circuit.It is from this second harmonic that the "Octa-Monic" gets its name. The idea of securingincreased selectivity, not through the use ofadditional circuits, but by the use of an inherenttube characteristic, is believed to be new.Reference to Fig.i shows the familiar gridvoltageplate-current characteristic of a standardvacuum tube. The curve follows a square law,and in doing such, causes some interesting results.1 1 is desirable when using such a tube for anamplifier to operate the grid voltage on a relativelystraight part of the curve so that fairlyundistorted amplification will result. For perfectamplification, this curve should be a straight line.The very fact that it is not, however, makes thevacuum tube a valuable device, as the non-linearperformance permits its use as a modulator,oscillator, detector, and a harmonic generator.It is its use in this last capacity that is leastunderstood and least employed.Now, if a special negative C bias isplaced onsuch a vacuum tube so that the grid variationstake place about some such point as A in Fig. i,the conditions will be favorable for the generationof second harmonics. Such harmonics arealways the result of unequal amplification in thetwo halves of a carrier wave. By operating atpoint A it will be seen that each positive halfof the carrier wave is amplified to a greaterextent than each negative half. Such an unbalancedcarried wave may be resolved into abalanced carrier wave of the same fundamentalfrequency plus another carrier wave of twice thefrequency. This is graphically illustrated in Fig.2 and is known as Fourier's Theorem. Brieflystated, it is as follows:advantage which the super-heterodyne possesses.Recently, super-heterodynes using higher intermediatecarriers than the broadcast frequencieshave been introduced to overcome the abovedetriment.It iseasy to see from this discussion that thereIf we have any single valued periodic curve,that is, one having only one value of the ordinateto one value of the abscissa, and repeating itselfat regular intervals, then, no matter how irregularthe curve may be, provided it does not exhibitI,is a real need for a new type of super-selectivecircuit that overcomes the side band limitation.With this thought in n ind, a series of tests hasbeen conducted during the last few months,which has resulted in the development of the"Octa-Monic" principle. This is a new systemfor obtaining a higher degree of selectivity andfollows from the considerations below. It hadlong been realized that selectivity was a geometricfunction and that placing one tuning circuitafter another createdthe geometric conditions.Naturally, every geometric function occurringin radio was then investigated with a view toemploying that feature for selectivity. One of themost promising was the generation of secondharmonics and it is this that forms the basisof the new RGS "Octa-Monic" receiver.FIG.IIt is well known that a vacuum tube has acurved characteristic unless a verv high externilFIG. 2

1368 RADIO BROADCAST OCTOBER, 1927discontinuities, it is always possible toimitate this curve exactly by addingthe ordinates of superimposed simpleperiodic or sine curves of suitable amplitudeand phase difference, havingwavelengths which are in the integerrelation to each other.Curve C in Fig. 2 shows the unbalancedcarrier wave in the plate circuitof the tube operated at point A onthe characteristic curve in Fig. i.Curve C is the equivalent of CurvesA and B in Fig. 2. Curve A is thefundamental carrier wave similar tothe one impressed on the grid of thetube. Curve B is the second harmonicwave.None of the graphic representationspertaining to the second harmonic revealthe secret of selectivity. Theymerely indicate that such a secondharmonic is present. The mathematicalequation outlining the performanceof the tube, however, does tellthe story. The equation for the unbalanced carrierwave shown by Curve C in Fig. 2 is asfollows:C = 2d (? + Eg + e ) e sin pt + cos (2 pt + X)The first part of the equation represents curveA in Fig. 2 the fundamental carrier. The secondpart of the equation represents Curve B in Fig. 2the second harmonic component.Now it will be noted that this second harmoniccemponent is proportional to the square of theinput voltage, e, and it is this squared functionwhich gives the geometric requirement for selectivity.Reference is here made to Fig. 3,whichshows a harmonic generator tube with the gridcircuit tuned to some frequency, F, in the broadcastband. The resonant curve of this tunedinput circuit is shown at A. Now the secondharmonic currents, 2F, in the plate circuit of thistube, are proportional to the square of the inputvoltages on the grid. As the incoming frequenciesare varied, slightly, from the true resonant valueof the circuit, the voltages on the grid fall offaccording to curve A. As the voltage has decreasedfrom its maximum, y, to the half waypoint at x, due to a change in frequency, a, thesecond harmonic current decrease is much morerapid and abrupt than in the case of the fundamentalcurrent, resulting in a very sharp resonantcurve in the plate circuit of the harmonic generatingtube. In these figures the fundamental andsecond harmonic have been plotted so that theyhave equal maximum amplitudes to show therelative sharpness of resonance.The next step was to incorporate such a principleinto a working receiving circuit. The firstroughly drawn, no attempt has beenmade to show relative amplitudeonly relative sharpness. In fact, quitea bit of energy is sacrificed in securingthe second harmonic component. Thissacrifice is more than justified becauseof the real selectivity obtained, andafter all, amplification can always beadded to a receiver. The additionalamplification is easily added by thearrangements shown in Fig. 5, whereone stage of radio frequency is placedahead of the harmonic generator tube.This additional stage does not needto be particularly selective as thesecond harmonic principle gives all ofthis necessary. For this reason, theadditional tube has been called a couplingor amplifying stage the circuitsbeing designed primarily for amplificationand not for selectivity. ItsFTC. 3input circuit is closely coupled to theantenna to give maximum energy pickupwith which to start. In order toattempt is shown in Fig. 4. Here the antenna gain some idea of the real improvement offered byis coupled directly to the tuned input of the the "Octa-Monic" as compared with tuned radioharmonic generating tube. The grid is tuned to frequency, reference made is to Fig. 6. This showsthe fundamental frequency of the broadcast the schematic arrangement of a standard twostagetuned radio-frequency receiver with thestation to be received. The second harmonicsare set up in the plate circuit where there is a resonant curves of the various parts of the circuittuned transformer, whose tuning condenser beneath and numbered to correspond. Curve Iresonates the secondary at the second harmonic shows the sharpness of tuning in the grid of thefrequency. Signals are changed to audio fre- first tube. Curve 2 indicates that the fundamen-quencies in the standard detector tube in thesame manner as any other circuit. Selectivitysuperior to that obtained by a two-stage tunedradio-frequency system was noted, although thesensitivity of the arrangement was much less.This would obviously be so because no amplificationis present in Fig. 4, and because theamplitude of the harmonic is less than that of thefundamental. In all of these diagrams, which areDetector TubeTo Audiotal currents in the plate circuit of the first tubefollow the same resonant curve. Of course, theenergy is greater in the plate circuit but thecurves have been drawn to the same scale for thepurposes of comparison. Curve 3 shows a gainin selectivity through the addition of the secondtuned circuit, while Curve 5 shows the finalgain in selectivity through the employment ofthe 3rd tuned circuit. It can be seen that onlyR.F. CouplingTubeHarmonic GeneratorDetectorTo AudioFIG. 5

OCTOBER, 1927 BOOK REVIEW 369FIG. 6To Audioband of the carrier frequency plus and minus5000 cycles to- insure good tone quality and10,000 cycles variation is a much smaller percentageof the second harmonic currents than ofthe broadcast frequencies. For example, at 1000kc. a io,ooo-band represents i per cent, whilein the second harmonic circuit this 10 kc. band isonly 0.5 per cent, of 2000 kc. In this unique waya high degree of selectivity has been secured witha faithfulness of tone quality that is remarkable.This RGS "Octa-Monic" arrangementis afundamentally new development. The existenceand generation of second harmonics has longbeen known, but the application of these currentsto the selectivity problemis a new feature.It has created a fourth and distinct type of radiocircuit.The next article in the series will discuss thiscircuit the resonant peak may be much sharperthe tuning circuits offer any selectivity whatsoever.interesting development and will contain plentyposition. So there is Felix's potential audience solicitation at Sunday dinner," is the attitude learned enough of a subject to be aware of hisin these groups and their fringes. He is qualifiedspeak to all of them, for he has himself Using Radio in Sales Promotion. fore freely criticised." CARL DREHER.expressed and implied on every other page of"ignorance." Broadcastingis free and there-Fig. 7 shows the schematic sketch of the than at broadcast frequencies without harming of information in connection with the building"Octa-Monic" system and the associated resonantquality. A tuned circuit must be able to pass a of the RGS receiver.curves beneath the several circuitsinvolved. Curve i indicates the sharpness oftuning in the grid circuit of the harmonic generator.This has the same shape as the first tuningcircuit in the system. In the plate circuit thesecond harmonic currents follow the resonantCurve 2, and the harmonic tuning circuit in theinput to the detector still further sharpen thisup to resonant Curve 3. This resonant curve issimilar in shape to the tuning curve No. 5, in thesystem. The resonant curves in Fig. 7 are drawnon the same scale for the sake of comparison. Itmust be remembered that Curve 2 representingthe second harmonic selectivity has much lessTo Audioenergy in it than Curve i.It would seem, offhand, that this excessiveselectivity in the "Octa-Monic" would raisehavoc with the side-bands, as is the case in tunedradio-frequency circuits. The very harmoniccurrents themselves, however, offer the solution.At the high frequencies existing in the harmonicFIG. 7Selling It by Radiobeen a broadcaster, advertising man, merchandisingconsultant, and writer; and incidentally programs is shrewdly analyzed in theThe reason for the fundamental similarity ofUsing Radio in Sales Promotion: By Edgarby McGraw- of RADIO BROADCAST.appeal to allhe is, among other things, a Contributing Editor second chapter. Almost all of them are plannedHill Book Co., Inc., New including the largestYork City. 386 The author starts with a resume of the sevenyearpossible audience. Artistic standards, not fun-pages. Price, $5.00.history of the broadcasting art, and in his damental program appeal, are the variablefirst chapter he sounds a note which recurs quantity. Almost all the stations are shootingIS not without a touch of embarrassment throughout the book; broadcasting isIT at the same target, but with guns of differentthat Iprepare to review this pioneer work on not for forthright advertising, but for securing calibre.the subject of broadcasting as an aid to merchandising.The author has written in kindly ceivers are purchased for entertainment and Station" and that on "The Broadcasting Sta-the good will of the consuming public. Radio re-In the chapter on "Building a Broadcastingterms of my own masterpieces on various occasions,instruction. A trade name, a brief slogan, a very tion" near the end of the work, Felix discussesand transported me over the highways in few words of product description, may be mixed technical aspects of the broadcast situation, suchhis private fleet of Minerva sedans. In finding with the entertainment and instruction, but Fe-as wavelength congestion, station organization,his work good, therefore, Ilay myself open to lix always has his eye fixed on a psychological operation, and the like. He does not attempt tothe charge of log-rolling. To preserve my honor, dividing line which cannot be crossed with either tell the reader how to build a station, and inI should like to pan the author and his treatise, propriety or safety. Broadcasting is primarily fact advises him against tryingit. What he doesbut he has done too effective a job. The book is for the advertiser who can afford to wait, who is to outline the formidable problems whichoriginal, informing, and vigorous. Its blemishes has the resources to build up public good will, must be faced, and the general economics of theare slight and will probably be visible only to who is not too short either in his bank account situation. In discussing operation he describesthe reviewers.or his patience. As for the little fellow who demandsthe functions of the various members of theUsing Radio in Sales Promotion is writtensales tomorrow morning Felix advises staff and the principles underlying their work.primarily for advertisers; it aims to instruct the him to take his money to the local newspaper. In many other chapters, as in those on "PotentialAudiences of Broadcasting Stations" andman who contemplates spending a part of his The Midwestern broadcasting station which Iadvertising appropriation for time on the air. am reliably informed at this writing, is selling "Selecting a Commercial Broadcasting Feature,"Throughout over the air by direct description, gasoline, Felix enters the engineering branch, and, dealingit names names, gives exampleswith field strengths and microphone char-drawn from experience, and answers the questionswhich must occur to the man who signs cancer and rupture cures, and a 5O-cent chickenmattresses, gloves, overalls, radio apparatus,the checks. What interests the client interests dinner, is outside of Felix's " acteristics, he exhibits only minor lapses frompale. He (the broadcaster)accuracy.the professional broadcaster equally, whetherdoes not earn the right to inflict selling Using Radio in Sales Promotion is written inhe (or she) owns, manages, operates, sells time, propaganda in the midst of a broadcasting entertainmenta business-like, straightforward style, but it isany more than an agreeable week-end not devoid of sharp hits and epigrams. I quote awrites publicity, or performs in the studio.advertising men are in a similar guest may suddenly launch into an insurance few: "An expert is usually one who has not yet

370 RADIO BROADCAST OCTOBER, 1927A DEPARTURE IN LOUD SPEAKERSThe Rola Model 20 combines a baffleboard loudspeaker of remarkable efficiency with floorscreen measuring three feet high by two feelwide. The price is $85AN "ACME" OFFERINGThis novel loud speaker makes useof a double cone arrangement, goodamplification of the low notes beingpossible on account of the free edgecones. The manufacturers statethat an output device is not necessarywith this loud speaker. Price$25.00THE A. K. CONEThe new Atwater KentModel E employs a novelmethod of cone suspension,permitting satisfactory respouseto minute vibrations.Price $30.00THE CROSLEYMUSICONEA baflfleboard effect is obtainedby the use of the tilttablesurface. Price $27. 50THE BOSCH'LIBRARYAMBATONE"TRIMM" CONCERTO'A $10.00 cone, fourteeninches in diameter. Theseven teen -inch cone retailsfor $16.00OPERADIOThe "* Junior" modelhas a 30-inch exponentialair column whilethe "Senior" has one of54-inches, The pricesare $15.00 and $25.00A NEW MAGNAVOXLoud speaker and B supply in oneunit, a. c. operated. A 210 typepower tube should be used. Theloud speaker is of the dynamic type.Price for the unit, $110.00IN GOTHIC DESIGNA beautiful and wellproportionedfree-edgeperiphery cone. Thereproduction**from thePeerless" is in keepingwith its appearance.Price $35.00FAD A "PEDESTAL*This is a twenty-two inchfree floating cone of attractiveGrecian design.The overall height ic fiftyfive inches. Price $50.00THE "CASTLE"A two-tone bronze reliefpattern enhancesthe appearance of thisTower seven teen-inchcone. Price $9.50

OCTOBER, 1927 1928 LOUD SPEAKERS 371GREBE "20-20"The numerals denotingthis model refer to thecone diameter and thefact that it is constructedat an angle oftwenty degrees. Price$35.00ALGONQUINA full floating coneof a moisture proofimpregnated fabric.The AlgonquinElectric Companyretails this cone at$15.00BALDWINA special unit is responsiblefor the goodtone of the Baldwin"99." This instrumentsells for $28.50ANOTHER ROLA ART MODELA large and effective baffle surface is responsiblefoi- excellent tone Quality. Rola manufacturesless expensive models, from $28.50 up. The oneillustrated is priced at $45.00UTAHThis $30.00 instrumentis of 5-plya t u r a 1 finishedwalnutAN INNOVATIONAn up-to-date post-warmap of the world surroundsthe Symphonic Globe louda $35.00 productraker, the Symphonic SalesCorporationA 22-INCH CONEThe new Sparton loudspeaker, a product of theSparks-Withington Company,retails at $30.00IN DISGUISEA cone loud speaker in tintableform the TeletoneModel 70. Price $40.00THE MOHAWK"PYRAMONIC."The pyramidal construction inthe diaphragm is responsible forvery excellent quality from this$25.00 instrumentTHE"ADVENTURER"Another bas-relief patternof the TowerManufacturing Corporation.The ship issuitably and vividlycolored. The price $9.50ANOTHER PEDESTALThe Haldwin loud s|H*:

SHOULD THE SMALL STATION EXIST!By JOHN WALLACEcase for the small broadcaster is seldom ourselves on good quality. KDLR has a studioheard, because he is small, possibly and 18 by 25THE by ourselves following Sabine'sbecause the public through habit and forformulas. For band concerts we have a bandshell,other reasons, directs its attention to the only in the state of North Dakota,largerthat will seat aand better-known stations. Has loo-piece band, built so that thethe smallbroadcaster a place? Does he serve a local need?point is 50 feet from the front of the shelland here we pick up every instrument with butHow can the small station better serve its public?An interesting letter from a reader in the shell can talk in a whisper and the "mike" willone "mike." The shell so built that a speaker intor at each end, every piece of equipment enough, and since they enjoy it they are entitledmeter-checked at both ends and we pride to it.Devils Lake, North Dakota, discussing this pick it up and put it through an amplifier attopic follows:any volume desired without its being overriddenby hiss.1 have been reading with a great deal of interestYou, living in a city with the choice of a scoreyour department in RADIO BROADCAST of fine stations at your command, find cause toand obtained very much enjoyment out of it. kick and kick loud, long, and lustily at whatNumerous things that you say however lead me you hear. Come out here once and hear one stationor possibly two, both in the same state,to believe that you are about as biased an individualas ever wrote.and after you are here awhile I guarantee youThe particular thing that seems to cause you go back home and enjoy what you hear.the greatest amount of worry is the small station.I own and operate a small station, as far rest of the world and try to do a little boostingThen after you are home give a thought to theas power output goes. Some of the things you and cease knocking that about which you apparentlyknow so little.say get under my hide. Picture yourself out herein North Dakota, living in a small town or on a hope that you have not been bored by theIfarm vainly twisting the dials looking for entertainment.None to be had. Then, "This is thing, you have a wonderful magazine, but dolength of this thing but allow me to say anotherKEJM The University of North Dakota" or WDAYor KFYR or KDLR as the case might be. A use a little judgment.programBERT WICK Operator, KDLR.of good entertainment for an hour or two comeson the air. You listen, you are pleased, youswear by the small station, you pick up a Mr. Wick's pointis well taken even if hepaperand note the many excellent does take us to task at the same time. In ourprograms beingsent out from a multitude of stations, none ofown defense, let us say that he overestimates ourwhich are heard here, except a few months in dislike of the small station. We have not saidwinter. Would you favor the abolishing of many harsh words about it. More than likelythe small station? Would you dismantle your he reaches this conclusion because of the factradio set in February and not use it again untilthat we ignore the small station in these columns.November? Would youifyou turned onyour set night after If we donight and neglect it too much, there arelisten for stationsthat cannot be heard? Would First, the small local stations, beingyou?two reasons.Or would you listen to the very excellent lowprogramsfrom our local small station?to enable fair comment. Secondly, local stationspowered, are difficult to "get" often enoughThe programs sent out here are not the high are of especial interest only to the persons withintype of the big Eastern stations but they fill their limited range and hence do not logicallythe bill. An example of our type of program, demand space in an article that considers radioMonday evening at 9:30-10:00 the OrientalTrio, the pianist a graduate of one of the nationally.largest Ourschools in the country, a student of a notedcorrespondent asks us: "Would you favortheteacher in Berlin, the soloist a former member abolishing of the small station?" Our answerof the isMinneapolis Symphony, the violinist a yes and no. For small stations situated as areformer member of the Detroit Symphony all those he mentions in his letter he gives an excellentvindication. There are long periods dur-doing their best. At 10:00 P. M. an hour of dancemusic played by an 8-piece organization composeding which it is impossible for isolated communi-of men who have been playing together ties to receive the distant stations, even thoughfor three years and who know and understandpowerful, with anymusic. At 1 1 :oo p. M. fifteen minutes of the satisfactory reception.finestkind of pipe organ music. And on a They are entitled to local stations, of lowWednesdayevening a program of band music played by a power, to fill in these hiatuses. Moreover theband of sixty boys, "The Governor's Boy Concertvery fact that the program is local must give itBand of Devils Lake" an organization of a certain interest to those in the hinterlandssix years standing under the leadership of the who take a keen interest in local things, in con-finest bandmaster in this section of the country trast to the city dwellers who don't know theirand playing overtures and marches of the highestclass. The soloist with the band is a lady whoapart-alderman's name nor the peoplement below. The farmers and other dwellers inhas recently returned from that famous musicthe Centerville area areschool in Philadelphia where you must havejust as likely to preferthetalent to get in. That was ourwares of Centerville's lo-wattprogram last week.broadcastingDaily we run the noon hour station to those of wcco asprogram playingthey are likely tothe finest available recordings of symphony prefer the Centerville Bugle to the Minneapolisorchestra and famous singers, played through Tribune. Probably they are personally acquaintedperformers who appearan electric pick up. Daily we broadcast the weatherreports and market information and the before the Centerville station's microphone, orstation is eagerly listened to.at least they know the announcer's cousinYou may wonder at our quality. We have theNellie or theirfinest and newest nephew goes to the same Districtschool as the Staff Organist's son. Hencetype microphones, the bestamplifying equipment that we can buy, testedand balanced pick uplines, a their interest in the localmonitoring opera-programis naturalTHE SMALL STATION HAS NO PLACE IN CITIESD UT we are allin favor of abolishing the small^ station from the metropolitan areas. If theHyde Park district of Chicago, say, wants topublish a little four-page newspaper to retailthe local gossip to the provincial minded of itsneighborhood, and to advertise the wares of itslocal drug stores and meat markets, well andgood. Nobody outside that section has to buythe paper, nor need even know that it exists.But when that same Neighborhood Associationstarts to operate a radio station to afford opportunityto the piano pupils of the neighborhoodand to peddle the aforementioned meatmarket's wares, it becomes, however low itspower, somewhat of a public nuisance. Evenwhere it doesn't actually interfere with the firstclassstations it needlessly clutters up the dialsand is an unpleasant distraction while tuning.This complaint holds also for stations in suburbsand in small towns within a hundred miles orso of some large city.We have never heard our correspondent'sstation KDLR; we hope to hear it when DX isagainpossible. Certainly the program he describessounds like a very creditable one. Mere magnitudeand wealth are not the only requisites fora good broadcasting station. While large financialresources must necessarily allow a station topresent more varied and elaborate offerings theydo not guarantee artistry in that station's modeof presentation.It is perfectly possible for some small station,somewhere, to achieve a reputation equal, oreven superior, to the large city stations. Whetheror not you like the "Little Theater" there is nodenying the fact that some Little Theater productions,financed on a shoe string, are superiorin artistry and in manifestation of good tasteto many of the costly Broadway productions.The same opportunity presents itself in theoperating of a small radio station. An individualgifted with good taste and a certain sort of geniuswhich we shall not attempt to label could, conceivably,operate a station in time which listenersthe country over would labor with flattenedears to pick up. He would have to be an individualof extraordinary personality and thatpersonality would have to manifest itself inevery detail of the programs he offered. He wouldhave to have complete supervision over everyitem he broadcasts and, essentially, do all hisown announcing. In contrast to the impersonal,routine, and frequently "high hat" manneraffected by the metropolitan stations, his modeof presentation would have to be decidedly personaland intimate. He would have to establisha very real bond between himself and his audience.The musical programs he offered wouldhave to express his own tastes, as would everyother sort of program he offered from time totime. And if he were a big enough man, his tasteswould be broad, and he would, in consequence,attract a big enough audience. He would nothave to have a lot of artists, but the few he hadwould have to be good, and show, in all theirwork, his fine Italian hand.His position as "editor" of all that his stationoffered would very closely parallel that famous

OCTOBER, 1927 THUMB-NAIL PROGRAM REVIEWS 373instance in the history of American journalismwherein an editor of unusual genius, though attachedto an unimportant newspaper in an unimportantMid-Western town, gathered to himselfsuch fame that his editorials were quotedthe country over and his newspaper even enjoyeda scattered circulation over many remotestates.And finally his reward would be consideredin the form of dross dollars about as great asis the financial reward of the operator of a LittleTheater.Why Not a Station Operated by aForeign Language Group?are several broadcasting stations,mostly among the smaller ones, devotedTHERE to some special group of listeners. Forinstance there are the two labor stations whichaim their output especially at the man in overalls;and then the stations operated by somereligious group, as the Roman Catholic andChristian Scientist. It has puzzled us, from timeto time, that no station has ever come into existenceoperated by a foreign born, or foreigndescended, group for the benefit of its fellowsin this country who cling to the mother tongue.While we have no statistics at hand tolend weight to this proposal, isn't it saidthat there are as many Italian speakingpeople in New York as in the city of Naples,and more Swedes in Chicago than in thecity of Stockholm? If these statements beexaggerated at least the "foreign-language"populations of these cities do run into largefigures. Chicago, besides its vast area aroundBelmont Avenue where one can examinethe store signs for blocks without seeing aname that does not end in -son, has populoussettlements of persons of Polish descent,Italian and German. These peopleparticularly the older generation, have recourseamong themselves almost exclusivelyto their former native tongue. Their sonsand daughters though they prefer theAmerican idiom, have, nevertheless beenacquainted with the second language sincechildhood. It seems to us they should beinterested in hearing programs conductedentirely in their own language, featuringartists and speakers of their race, and ingeneral devoted to their racial interests.The Great War is remote enough now sothat no idiot would be likely to call themanoeuvre unAmerican.advertising. If the bonds of a common fatherlandhold these people close enough together tomake a newspaper self supporting,it wouldseem, by analogy, that an unpretentious broadcastingstation would not be an impossibility.The value lo those, like ourself, who do theirbest talking and listening in the American patois,would be, perhaps, not large. But it wouldbe a great thing for students of foreign languagesto have a station they could tune-in on, on occasions,to supplement their reading and writingwork. Moreover it would give a pleasant cosmopolitantang to the air. And picture the delightof a listener out in Kansas tuning throughto some Italian station in New York and imagininghe had got Rome!,.,,:Thumb-Hail Reviews>E WRITE in themiddleof the summer,at a time when DX conditions are attheir worst, so instead of trying to reviewsome static-mingled distant squawks weshall confine ourself to considering some of thechain features which are received over a wide area.The summer season, may we say, has beenbetter than any previous summer in radio'sAN ESKIMO LULLABY AT WGYlone, When You're in Love, Listening, HonoluluMoon, and Selections from the "Red Mill"following each other in sentimental succession.But Erva Giles has a beautiful soprano voice forthese songs and the Radiotron's much featuredVaughn De Leath always delights us with hermellow alto and throaty half-spoken passages.I PAN A TROUBADOURS (Red Network) continueto be one of the most reliable orchestras that areto be heard weekly. Their plucked instrument,section (they have another section strings)continues to lead in its field, which is probablyto be expected considering all the practice ithas had over the past two and a half years.ELK'S MALE QUARTET (Blue Network) Thequartet is an unfailing radio standby. Mayhapour interest in the quartet springs from thefact that every one of us is a potential singer ina quartet and stands ready to contribute hisservices thereat under proper stimulus, such asa shower room, a clam bake, or a couple of stiffsnorts. Be that as itmay, the Elks' is an excellentquartet.CONTINENTALS (Blue Network) The Continentalsis a very able organization made up of achorus and soloists under the direction of CesareSodero and specializing in opera selections. Thesoloists include Astrid Ejelde, soprano andan excellent one; Elizabeth Lennox, contralto;Julian Oliver, tenor, and FredericBaer, baritone. The programis well selectedand does not stick too exclusively to thethreadbare arias. Tuesday evenings at nineEastern time.STROMBERC-CARLSON ORCHESTRA (BlueNetwork) This isGeorge Olson's band,playing under a trade name, and a first rateband it is, as others than ourself will assureyou. Perhaps much of the credit for thesmooth and beguiling manner in which itplays is due to its orchestrator, one EddieKilfeather, who specially arranges many ofits numbers.STADIUM CONCERT (Blue Network) TheStadium concerts occupied, as last year,first place on the list of summer offerings.We were afforded mingled emotions in hearingour M r. Stock as guest conductor of thePhilharmonic musicians, what with the currentprospects of having no Chicago SymphonyOrchestra this coming season, due towage disputes. (We wonder why the OrchestralAssociation didn't offer to sellIn the Schenectady studio, Trixie Ahkla, Eskimo, sings a good broadcasting privileges to meet the in-Ihere have been foreign language pro- night lullaby for her two sons Miles and Billy. Up North, where creased demand for funds). To quibblegrams from various stations in the United the night is long, this domestic duty need be discharged only about minor points: we saw no reason whyStates, but only intermittently. Someonce a French programs were broadcast by a Newyearthe announcer should descend from his ponderousand dignified perch at intervals toYork station, wiuo in Chicago has for nearly two history. Many featuresyears broadcast a program in Swedish quite up to winter time refer to one of his fellow workers as "Jimmy." Ifevery Sundaymorning from 8:35 to 10:00. Inquiry at WIBO the annual vociferous protestation that "therestandards were heard. The stations supported they will be high-hat let them be consistent.reveals the fact that this program has been enthusiasticallyreceived by Swedish people, not ferent agencies are engaged in orchestra under the direction of Rosario Bour-is noCITIESsummer SERVICE CONCERT slump in radio!" So many (Red Network) Andif-only in Chicago but re-iterating thisby long distance don and a chorus called the experts inCavaliers. Butphrase every year, particularly radio manufacturers,that it occurs to us that they do say about them? we have exhausted ourpro-whatWisconsin and Minnesota both ofshallwhich westateshave a large Swedish population. The same stationrecently inaugurated a program in German exists. If it does exist it is because radio listentesttoo much, and that a slump none the lesscritical imagination. At any rate they are consistentlygood. They specialize in the lighteron Sunday afternoons from 2:30 to 3:30.ers have been able to discover other doings more composers, Herbert, Friml, Straus, and so forth,1 here is no doubt at all that a with other occasional novelties.foreign languagestation, properly situated, would enjoy a largeenough audience to make its efforts worth while.Nor does there seem to be much doubt that itcould get artists; suppose an Italian stationsent out a call for Italian singers! But there maybe some question as to how well it could supportitself. Perhaps here is the rub and the reason thatnone has so far appeared. However the foreigncommunities in the large cities manage to supportflourishing newspapers, which are packed withintriguing than sitting in the front parlor of awarm summer's evening, and not because the stationshave not made an effortto please.THE RADIOTRONS (Blue Network) These artistsin their program of alternated orchestraand voice strike a mood that nicely ties thewhole shebang together. In the case of the programwe have in mind the flavor persistingthroughout was a decidedly saccharine one;such numbers as Tumble Down Shack in Ath-ROYAL HOUR (Blue Network) After havingdistributed roses the length of this column it isnow our privilege to get mad. The Royal Hour'sthirty-minute broadcast is a throw-back toradio's worst days. Advertising isjammed inso thickly that the musical part hardly has achance to stick its nose out before it is drownedin further advertising. Every number on the programis introduced with a labored reference tothe sponsoring company and its product.

Your A* C. SetHow to Search for DefectsWhen Your A. C. OperatedReceiver Qoes DeadEDGAR H. FELIXCALL THE SERVICE MAN"Shut off the power, call for a trained professional service expert, and leave the set alone"the advice to perplexed owners of a. c. sets in time of trouble by the head of the servicedepartment of one of the largest radio manufacturing concernsTHE head of the service department of oneof the largest radio manufacturing concernsin the country was asked at a meeting recentlywhat advice he would give to the ownerof an a.c. operated set which has suddenly goneout of order."Shut off the power, call for a trained professionalservice expert, and leave the set alone,"was his answer. "The troubles that arise witha.c. receivers are few and easily remedied by experts,but an experimentally inclined novicewho doesn't know what he isdoing can actuallydo great damage if he starts to tinker aimlessly.When a person gets sick, he calls on his doctor;when his automobile goes out of order, he bringsit to the service station; but when a radio setgoes wrong, three out of five listeners proceedboldly with soldering irons to change wires, toshort-circuit transformers, to reverse connections,and to apply high voltages here and there,just to find out what happens. A competentman, familiar with the functioning of radio setsand their associated power supply, makes aninspection, analyzes the difficulty, and replaceswhatever is necessary in a few minutes at a minimumof expense; a venturesome experimenterusually tinkers until he has done serious damage,then calls in an expert and, when he gets the bill,wonders why radio repairs are expensive. Thereisnothing mysterious or really troublesomeabout modern a. c. sets, and servicing them isusually a matter of the utmost simplicity."Careless tinkering may prove an unhealthypastime for the would-be radio expert who isaccustomed to learn his radio by practical experience.Large condensers of several microfaradscapacity, charged to 500 volts, may impress theireffectiveness upon him with such force that hewill find himself involuntarily, violently, and uncontrollablyseated on the floor several feet fromthe radio set. But, if he temper his examinationwith knowledge, most of the likely faults of a. c.operated sets can be readily identified by theirsymptoms and, in some cases, the necessarymeasures for repair taken.Servicing the a. c. set has brought a new dignityto the job of repairing radio sets because ithas converted the receiver to an electric powerdevice of considerable magnitude. Indeed, somarked is the change involved in the engineeringdesign of a. c. sets that some of the earliermodels, designed by radio engineers, failed principallybecause of inadequate knowledge ofpower engineering.The excessive service grief which attendedsome 1925 and 1926 a. c. sets has been largelycured by the application of the principles ofpower engineering to radio. These pioneer modelstaught us the stresses and surges to which thefilter condensers are subject with the consequencethat the latest receivers have condensers of considerablygreater voltage-carrying power thanthose of past seasons. New rectifier tubes ofgreatly increased capacity have solved voltageregulation and life problems, while such refinementsas ballast tubes and regulator tubes givethe designer wide latitude in his work. Also wehave new types of tubes which avoid the use of arectifier by using alternating current for the Asupply. All of these advances have brought usto the threshold of a new era in radio set designand the elimination of the burden of maintenanceattention. Given capable engineering and adequatequality of materials, the modern alternating-currentset, whether it be of one type oranother, isreasonably reliable and a marked improvementin convenience over its less advancedpredecessor.Certain parts of the alternating-current receiver,however, depreciate with long use. It isno more possible to design a wear-proof radioreceiver than it is to design a wear-proof automobile.Vacuum tubes lose their emission and condensers,unless of tremendously greater voltagecapacity than their service requirements demand,eventually break down. 1 1 is only a matterof time, however, when the service attentionrequired by a.c. sets will be reduced to a matterof annual inspection to replace rundown tubes.Indeed, some of the latest sets have actuallyreached that stage.But we cannot expect a radio receiver to requireno attention whatever. Filter condensersare really moving parts. They are constantly subjectedto considerable voltages, and are chargedand discharged rapidly and continuously. Theatomic structure of their components is constantlystrained so that in time they become lesscapable of resisting these rapidly changing voltagestrains. The experience of the last two yearshas resulted in the widespread use of bypass andfilter condensers which will, under ordinary conditions,serve for a period of years, rather thanmonths, as was the standard heretofore. To mentionbut one, ifyou have opportunity to look atthe output condenser in the power supply of aStromberg-Carlson a. c. receiver, you will observethat its size compares with that of condensersused in receivers of a year or two ago almostas does a match box with a steamer trunk! Expensiveas these improvements are, they are aneconomy because they approach the ideal"plug the set into the light socket and the receiverisready to operate for a period of yearswithout attention."TWO TYPES OF A. C. SETSIN GENERAL, there are two outstanding typesA of alternating-current sets first, those inwhich the alternating current of the line is convertedinto direct current by rectifiers, smoothedby filters and then used to power filaments of themore familiar type of vacuum tubes and, second,those with tubes utilizing raw alternating current,either of the rugged filament or heater elementtype. Already considerable experience hasbeen gained with the first type of set and itsservice and engineering difficulties are quitewell known. With the second, there is less experience,and which of the two kinds will provethe ultimate winner is hard to say at this writing.Tubes using raw a. c. for their A supply neverthelessneed d.c. for B and C power, and thereforea rectifier of some kind isnecessary unless A andC batteries are employed. The use of these tubesrequires the introduction of an appreciable 60-cycle a. c. current right into the radio receiver,in and near the radio-frequency elements, introducinghum difficulties, and the life of the tubesunder ordinary service conditions is yet to bedetermined. Considering that RCA, Cunningham,McCullough, Van Home, and others aremaking a.c. tubes, it is certain that there hasbeen much fruitful development work done sincethe first of this- type' of tube was introduced severalyears ago.As to the first type of receiver, that is, those usingconventional tubes, usually of the 199 type,with filaments in series and powered by a rectifiersystem, there is a wealth of practical experiencein servicing them, gained during the last twoseasons. The largest sellers in this class have beenthe Radiola super-heterodyne outfits used inconnection with the 104 loud speaker and ana.c. rectifier power unit; the Garod, and theZenith. By consulting not only manufacturers

OCTOBER, 1927 YOUR A. C. SET 375but the service heads of responsible dealer organizations,possible to learn what theservice problems in connection with the sets are.The author is particularly indebted to the R. T.M. Service and to Mr. H. T. Cervantes of HaynesGriffin Radio Service for much of the informationwhich follows, based on their experience withthousands of these sets in the New York area.The procedure for locating trouble, the significancesymptoms, and the remedies, aredescribed with a view to aiding the set ownerdetermining whether his set requires the servicesof an expert service man or whether asimple adjustment will put it back in service.Breakdowns with a.c. sets generally impose astrain on the rest of the outfit and, consequently,a certain amount of knowledge of possible difficultiesmay avoid more serious damage.When the set goes dead, either shut off thepower until the service man takes charge, or elseimmediately determine whether the rectifiertubes light and, if the set has them, note also ifthe ballast and the regulator tubes glow. If theseappear to be functioning, reduce the filamentvoltages by means of the filament rheostat.Sets with filament rectifiers do not, of course,give visual indication of their condition and inspectionprocedure, withsuch rectifiers, is to test with a rectifier tubeknown to be good.Next check the condition of the radio, detector,and audio tubes of the set. This is easy, if youcan plug in phones in the detector and audiostages. A signal in the phones indicates that allthe tubes supplying them, including radiofrequencyand detector stages, and sometimesthe first audio stage, are in good working order,as is the power supply for all but the final outputtube.1 n absence of this convenient test, examine thetubes in the radio receiver. If necessary, darkenthe room to do so because tubes of the dry-celltype do not generally light very brightly. Withsome series filament receivers, all the tubes goout when one filament fails. With others, a resistoris used in parallel with each filament as aprotective measure and it will pass enough currentto light the remaining tubes in the receiverwhen one or two filaments are burned out.If you do not locate the tube out of order byinspection, substitute a good tube for each onein the receiver, one at a time, remembering, ofcourse, the first instruction to keep the filamentrheostats low.In the case of sets without the filament resistorsin parallel, an even more serious strain isimpressed upon the filter condensers when oneradio tube goes out, unless a regulator tube isemployed. In some cases, when the filament loadis removed from the rectifier system, the voltagebuilds up greatly, sometimes sufficiently, in fact,to cause the breakdown of filter condensers.The capable service man who, from a briefinspection of the receiver, decides that one ofthe radio or audio tubes may be dead, tests thetubes with a tube tester rather than placing hisreliance upon the power supply of the set to doso. This avoids undue overload of the rectifiercondensers. The manufacturer's instruction bookoften explains the best course to follow when thereceiver goes dead and, understanding the reasonsfor it, the reader will not leave his power supplyturned on if his tube filaments do not light,should the manufacturer advise him not to do so.The best test of radio and audio tubes is to use atube tester or to replace the entire lot. Otherwisesubstitute a good tube in each socket, one at atime, leaving the remaining tubes in their sockets.Assuming that rectifier and ballast tubeslight and that radio and audio tubes havebeen proved good, the next thing to examine is tubes.show begunservice atthanrectifierof oneother remains looksload oftube, whichoverloading.of thewhen bothdue to anbroken-downthis occur,service atoverload replacementis atechnician.regulatorservice manthe substitutioncheck the conditionregulator voltagecondenser,tubes, atube, theIt iskeep theloud signal brilliancyis disconnectedtube whichfrequentis needlessconnections,power line,contacts withreproducer,specificallythe kindincreasing rarenessdesignhowever,hum in theInblueonce,replacementtubes,ofnormalthebecomesrectifierrectifierunusualonceonjobtubes,is usuallytube failingthevoltageortroubleslostof most cases,or purpleto leak. Ifas thereofmaythem turnsits normalsimple indicationhas lostset isbeingredThe remedytubetubesloadbypass orthe setbecausethe rectifierof thefor an experiencedthe simplestof acf thedoes notpink, it issupply, duefailure ofballastelements ofpurpose ofsupplycontinuedof itsanyoccurs indicatesencounteredto go intodefectiveemissionsocket, incorrectand otherassignabledifficultiesas thereceivingto mentionreproducer,if the rectifier tube or tubes aglow, it means that theyso, place the set out ofis no other repair possiblethe rectifier tubes.When there are twohappen that the platesbright red while thecolor. Usually, this is athat the tube whichits emission and the entiredrawn from the otheras a consequence of thisisobviously replacementwhich does not overload.On the other hand,become bright red, it isupon them, usually afilter condenser. Shouldshould be placed out of this places an extremetubes and the only remedyservicedefective condensers. Thischeck which ain aWith those sets usingposition to apply at once isgood regulator tube totube in service. When thegive a colored glow, eithernot receiving its necessaryto the shorting of a bypassone or both of the rectifiertube or a radio or audiowhich are short-circuited.the regulator tube toconstant. A prolongedstrong static may increaseglow. But, if the antennathat it is defective.flashing of the regulatorThis completes the onlywith a. c. sets. Itthe usual defects looseplug or flexible cord to of power tubes, dirtyadjustment ofdifficulties which are notto the a. c. set. They arewhich occur withmechanical and electrical sets improve.It may be worth while,that a sudden increase ofwhich has previously been quiet, may be due tothe breaking down of a bypass condenser, achange in the load conditions of the power line,or reversed line connections. The latter is sometimescorrectable by pulling out the plug, givingit half a turn, and re-inserting it. The power-linenoise may require the attention of the powercompany as, quite frequently, it is the result ofusing an appliance in the immediate vicinitywhich sets up power surges in the line. These canbe cured by installing an interference preventorat the device.From the foregoing, it is obvious that there isnothing unusual or startling about the servicerequirements of a.c. sets. They introduce newproblems but, once these problems have becomefamiliar, they will not cause any serious modificationsin radio servicing. The radio trade is learningthat it must take its service responsibilitiesseriously while the consumer is recognizing thatservice issomething which he should pay for,just as he does when he has his watch or automobilerepaired. Free service has worked as muchharm for the consumer as it has for the industryitself, because dealers giving extensive free serviceultimately fail in business. And there canbe no redress when the dealer has gone out ofbusiness. Amateur servicing with power sets,also, may result in more serious damage, just asdoes inexpert tinkering with an automobile.Just why there is hesitancy in admitting thesesimple facts is a little hard to understand, since,with a little consideration, anyone will understandthat free service, inexpert service, andpromises of perfect reliability do not promotesatisfaction to the radio user.It is premature to set up rules for the selectionof a. c. sets at this stage because the relativemerits of the various a. c. systems have not yetbeen fully proved by user experience. One of thesafest guides is to consider the engineering reputationand stability of the manufacturer and theservice reputationof the dealer from whom theset isbought. A manufacturer who has a reputationworth losing will not skimp by using acheaper filter condenser in the hope that it willnot break down prematurely, nor will a dealer ofestablished standing in his community jeopardizehis standing by taking on a line without adequatetest and engineering examination. The dayof the a. c. set is here. It means simplified radioand adequate power, essential to beauty of reproduction.It means a broader market for radioreceivers, with the inevitable consequences oflarger production and more radio for the money.MAKING TESTS ON AN A. C. UNITThe two-microfarad condensers on the RCA 104 loud speakerpower unit are here undergoing tests for possible defects

AS THE BROADCASTER SEES ITGoing to Jail for Radio in GermanyINTHE United States, a good many, broadcastlisteners are in jail,but not for listening tothe programs. They went to prison first andlistened to the radio afterward, broadcastingbeing one of the inducements offered in all upto-datepenitentiaries. In Germany, however,radio has been the direct instrumentality wherebyone gentleman went behind the bars. It appearsthat he was a Scbwarfboerer, which means,literally, a black listener, i.e., one who neglectsto pay a fee and secure a license for his receivingset, as required by German law. The first timethis recalcitrant BCL was caught he was finedand his set confiscated. The second time theauthorities, with due process of law, clapped himinto the jug for three weeks. If they catch him athird time presumably he will be tried by a courtmartial of studio managers and shot some GreenwichMean Time morning.As a practicing broadcaster, I regard this incidentas a bad precedent, and am relieved that itoccurred in a foreign country. For, if a broadcastfor a little radio boot-listener may be sent uplegging in this style, it is only a matter of timewhen the broadcasters themselves will spendtheir week-ends behind stone walls with spikesand sentry boxes on top. A program impresariopermitting one of his flock of baritones to sing"Rolling Down to Rio" will be sent away forsix months. The singer himself will merely receivea black eye at the hands of one of the catchpolls,for delicate psychological tests have provedthat all baritones are subject to an irresistibleimpulse to warble this tune. When one of thewater-cooled tubes lies down in the middle of aprogram, interrupting the festivities for a minuteor so, the engineer of the station will be set tobreaking rock for one year. When the transmitterdeviates from the assigned frequency, the jollytechnician will be separated from his wife andchildren one year for each kilocycle high or lowand if another station has been heterodyned theowner thereof will be permitted to extract theoffending engineers' teeth. This may seem acruel, unusual, and hence unconstitutional punishment,but it is a sound maxim of law that astatute may be constitutional in one age and unconstitutionalunder later circumstances, andsome judge may reverse the process and decidethat, as broadcasting was not known to theFounding Fathers, new and appropriate punishmentsmay properly be devised for erringbroadcasters. On this principle, announcers whoread telegrams of appreciation to the radio audiencewill be forced to eat a pound of coarselyground Celotex. Announcers who read their ownpoetry over the air will be thrown to the tigersin the nearest zoo, thus relieving the tax-payersin two ways.Some of these penalties,Iadmit, appeal to me,and I have derived pleasure in contriving them.But, as Isaid, disapprove the I principle, sinceI am a broadcaster myself, and might be one ofthe first to be dragged to the hoosegow. thereforeappeal for moderation in this instance, I andshall telegraph to my Congressman requestingthat our government make representations totheReich on behalf of the imprisoned Scbwar^hoerer.Radio's "Aristocracy of Brains"IOFTEN reflect on the melancholy fact thatthe men who really made radio, the Marriotts,Alexandersons, Fessendens, Hogansand the rest, are not as well known as the morepopular announcers of fifty-watt stations. Comparedto the coruscating luminaries of the networks,like MacNamee and Cross, the engineersdo not shine at all. For this there are, of course,sufficient reasons, psychological and sociological;one might as well lament that Dr. G. W. Crile isnot as well known a man as Babe Ruth. I shallnot waste my tears in this cause, yetI cannotrefrain, coming down to cases, from pointing anaccusing finger at our contemporary and friend,Popular Radio, which on Page 402 of its April,1927, number, prints a picture with the caption,"A Group of Radio's 'Aristocracy of Brains.'The description which follows is reprinted verbatim:Dr. Ralph Bohn (in front of the desk) is receivingthe Liebman Memorial Prize of the Instituteof Radio Engineers from Mr. Donald McNicol,former President of the Institute. Dr. Bohn himselfis the new president. At Mr. McNicol's leftis Mr. John V. N. Hogan, Contributing Editorof Popular Radio. Next to him is Mr. R. H.Mariott. Behind Dr. Bohn are Professor MichaelI.Pupin, of Columbia University, Mr. L. E.Whittemore, and Mr. E. F. W. Alexanderson,well-known inventor and radio engineer of theGeneral Electric Company.Children, what iswrong with this description?In the first place, the President of the Instituteof Radio Engineers is Dr. Ralph liown. The prizeis awarded each year in memory of ColonelMorris N. Liebmann. Mr. Hogan's middle initialsare y. L. Robert Henry Marriott, the first Presidentof the Institute, spells his name with two"r's." Finally, the gentleman in the picture justbehind Professor Pupin looks suspiciously likeDr. J. H. Dellinger, and not at all like Mr.Whittemore. The total of errors appears to befive. 1 call loudly for a more flattering vigilancein such matters on the part of Messrs. KendallBanning and Laurence M. Cockaday. They runaltogether too good a magazine to permit sucha high concentration of mistakes to the cubiccentimeter of printer's ink to pass unnoticed,especially in reference to the Brahmins of theradio art.XXMemoirs of a Radio Engineer.MY FIRST assignment at the Aldene factorywas in the test shop. This was agood-sized room in the old stone building,which later became merely an annex to themodern factory structure erected to fill the wartimerequirements of the Army and Navy. Alongone wall there was a switchboard controlling thesupply of a.c. and d.c. to various outlets. For therest the room was crowded with quenched sparktransmitters of all sizes from one-quarter to fivekilowatts, miscellaneous apparatus in variousstates of disarray, work tables, meters, and afew men: W. H. Howard, the Chief of Test;Baldwin Guild, now practicing patent law withPennie, Davis, Marvin, and Edmonds; my presentcolleague O. B. Hanson; a tall gentlemannamed Lieb; a more medium-dimensioned gentlemannamed West, and myself.Imay haveomitted someone, but I think this comprised thelist in May, 1917.paratus.tween the routine test functions of the department.Inasmuch as I was known to possess someThe engineering staff of the Marconi Companyhad the privilege of using the facilities of the testroom for experiments when they could get in.By experiments do not mean research on electronvelocities or anything else at all recondite,but merely such incidental tests and measure-Iments as always accompany the design of ap-This work had to be sandwiched in be-engineering training,as a sort of assistantI was assigned temporarilyto engineers who requiredwork to be done in the test room. My first jobwas handed to me laconically by Mr. Woodhull,one of the transmitter engineers. A five-kvatransformer was trundled into the test shop anddumped off. "Measure the iron losses," said Mr.Woodhull, and disappeared.Igazed at the transformer. It contained plentyof iron in the form of a shell core, and no doubtthere were losses. I could identify the primaryleads, which were to be fed at 1 10 volts a.c., andthe secondary terminals, which were expected todeliver juice at 10,000 volts or so to the quenchedspark gap of the five-kilowatt transmitter. Ihad never measured the iron losses of a transformer,but 1 had some vague recollection, from

'OCTOBER, 1927 TECHNICAL PROBLEMS FOR BROADCASTERS 377and But what is aof a small transformer, I should not have beensurprised. A bonehead idea? Certainly, at that plate current-grid voltage characteristic. Theplace time. good engineer?One who has, in the course of practice, got ridof a few thousand of such bonehead ideas. Hegets paid largely for the relatively accuratejudgment of physical magnitudes (alwayschecked by measurement) and economic results(always checked by the balance sheet) which liehas been able to put in their place.( / o Be Continued)--f- E=960V.Technical Problems forcasters. IVBroad-FIG. ITHE plate feed of a fifty-watt (oscillatorrating) tube used as a reactance-coupledmy studies, that the procedure was to put ratedamplifier in a broadcast transmitter isvoltage across the primary, leave the shown in Fig. i. Plate potential is supplied by asecondaryopen, and measure the power input with a wattmeterunder this no-load condition. So I lookedstorage battery with an output voltage E of 960volts, the internal resistance being negligible.The reactor in thearound for a wattmeter. The only one plate circuit has 50 henrysI couldinductance and the d.c. resistance RL is 1320find had a full scale deflection of 7.5 kw., so Ihooked it up and threw the ohms. The switch. resistance dropNothingdesignatedIhappened. disconnected the wattmeter andby VL, and this will necessarily depend on themean current plate current lp which is indicatedbyamilliammeterAin the plate circuit. This platecurrent varies with the negative grid bias EGinstrument; it read several kilowatts. Iput itback in my circuit and tried accordingagain, still withoutupper characteristic curve ofFig.results. After an hour or so Woodhull came backproblem Given is, a safe plate dissipationand wanted to know what the iron losses of 70 watts for the tube in question, whathisis the minimum allowable negative gridtransformer were. With much embarrassment Iunder the conditions shown?confessed that I did not know, and showed himmy predicament. He looked over the circuit,Solutionand then glanced at the wattmeter. The scale We are told that 960 volts is the steady outputmade him laugh. "The iron losses are only of thepotentialorder of a hundred watts," he told me. "Youstorage battery under all conditions,since its internal resistance may be neglected.can't read that value on this scale. Get a o.;-kwHence, in order to find the actual voltagemeter out of the storeroom and try again." VP on the plate of the tube, all that is requiredFollowing these directions, 1 measured the iron is to find the voltage drop along the reactor forlosses of the 5-kva transformer at 70 watts, ifI remember the figure correctly. Then we wentahead with some other tests involving loads.plifier of the type shown is the product of theThis incident illustrates what the engineeringstudent just out of school is up against. Hemean plate current and voltage, as indicated byd. c. instruments in the circuit. We may thereforeusually has only a vague idea of magnitudes. 1 draw up the following table:had studied under first-rate teachers and my EG IPVi. VP WPpreparation in some directions, was not at allMill -bad. But there were numerous other fields inVolts Amperes Volts Volts Wallswhich Ireally did not know whether the answer 30 94124 836 78.535 83105 855 71.0would come out in millimeters or meters, or watts 40 72.5 95.5 864.5 62.5or kilowatts. If that wattmeter had swung up to 45 6281.5 878.5 54.4a reading of a kilowatt or two for the iron lossesThe first two columns are obtained from thetested it on another set which was under load.There was nothing obviously wrong with thevarious plate currents, and subtract these valuesfrom 960. The plate dissipation Wp of an am-VL column follows when the value of plate currentin each case is multiplied into 1320, the d.c.resistance in ohms of the reactor, giving the directvoltage drop across the winding. Subtractedindividually from 960 volts, these valuesyield the actual plate potentials corresponding tothe various grid bias figures. The plate dissipationis then calculated in each instance as theproduct of the Vp and Ip. As it happens, theplate dissipation results are numerically of aboutthe same order as the plate currents in milliamperes,so that they may be plotted in the formof the lower curve of Fig. 2. (This is an accident,resulting from the fact that the plate potentialsare near 1000 volts, but of course an independentcharacteristic could be drawn in any case.) Fromthis curve we note that 70 watts dissipation correspondsto 35.5 volts negative grid bias. Theanswer to the problem is, therefore, that 35.5the minimum allowable bias to be usedvolts iswith the tube in question if the plate is not to beoverheated.Section of the American Institute of ElectricalEngineers on Oct. 17, 1923. Reprinted May, 1924by Western Electric Company, Inc. (Bell TelephoneLaboratories, Inc.).A THOUGH telephone wires used in connectionwith broadcast transmission arein general not utilized for other communicationservices during program periods, technicalbroadcasters will find it instructive to learn somethingabout the multiplication of channels onexpensive long distance circuits by the use ofseparate frequency bands for different purposes.Doctor Jewett, who is himself responsible formuch of this development, has outlined the mainfeatures in this paper.r\ r\\jFIG. 3~rrvrv.n n ../rv.rv../n nn.The first point which concerns us is the analysisof a square-topped wave, reproduced here asFig. 3. Such a wave is produced in a direct currenttelegraph system which has neither capacitynor inductance, as the circuit is made and brokenby a key. It may be established mathematicallyand graphically that such a square-topped waveiscomposed of a continuous direct current anda number of sine wave alternating currents, comprisinga fundamental frequency correspondingto the keying frequency, and, theoretically, aninfinite number of odd harmonics. Fig. 3 showsthis d.c., and the a.c. components up to the eleventhharmonic, with the resultant wave form ineach case, and the ideal rectangular shape whichis secured when all the harmonics are preserved.Fig. 4 is a diagram showing the same componentsin their relative amplitudes. If the current at thereceiver is to be a strict reproduction of that atthe keying end, frequencies considerably higherthan the keying frequency must be transmitted.With hand sendingit may be necessary to passover the line frequencies as high as 40 cycles,to preserve the wave shape. With a multiplexprinter the range is preferably extended to 100cycles per second. Even in telegraphy, we note,accurate reproduction (what we call "good quality"in broadcasting) requires widening thefrequency band.Instead of keying a direct current for telegraphAbstract of Technical Article.VI50 605fi 30"Making the Most of the Line A StatementReferring to the Utilization of FrequencyBands in Communication Engineering," by Dr.Frank B. Jewett. Presented before PhiladelphiaOF 3F 5F 7F 9Fi11F 13FFREQUENCYFIG. 4

378 RADIO BROADCAST OCTOBER, 1927communication, we may make and break analternating current carrier. The resulting waveis shown in Fig. 5, the carrier being assumed toobey a sine law, and the line to be without inductanceor capacity. This wave may be resolvedinto a fundamental and harmonics, as shown inFig. 6. The difference between Fig. 4 and Fig. 6is that in the former (d.c.) case the harmonicsare grouped in ascending order on the positiveside of the hoizontal axis, starting with thefrequency O, which is the direct current component,while with an a.c. carrier the harmonicsare grouped on either side of the carrier fre\quency. In the latter method we employ a processof modulation and remodulation (now more>i

Home^Constracting Transformers andThe Second of Two Articles Intended to Obviate Tricky MathematicalCalculations when Building These Units The Design of Choke Coils, andthe Actual Construction of Both Chokes and Transformers, Is DiscussedBy HOMER S.DAVISCHOKE coils are used in radio work chieflyto introduce opposition to the flow ofalternating current, while at the sametime allowing direct current to pass easily. Ingeneral, the lower the frequency of the alternatingcurrent, the more the inductance required.At radio frequencies, air-core chokes mayprovide sufficient opposition, but at audio frequenciesand for smoothing out the ripple inpower-supply units, an iron core isprovided tomake possible a greater inductance in a morecompact unit, since the magnetic flux will flowthrough iron more easily than through air.A different situation exists in the core of thechoke coil than in the transformer core. In thelatter, the magnetic flux due to the alternatingcurrent has the core all to itself, while in thecase of the choke it has to share the core with theflux due to the direct current. To make certainthat the direct current flux does not saturatethe core, an air gap must be placed somewhere inthe core. This greatly complicates the design,and a reasonable length of gap is difficult tomaintain. Too great a gap will reduce the inductanceand therefore require a larger choke forthe same amount of inductance, while too smalla gap will increase the harmonics, thus impairingthe filtering action. It is generally agreed that agood value to use is one that uses up aboutninety per cent, of the magnetizing force. For anordinary silicon steel core this means a gap about0.005 inches long for each inch of core length.The actual value to give best results can bedetermined only by trial with the other apparatuswith which the choke coil is to work. Only thecore type of construction will be considered inthis article, as was done in the case of the transformer,design data for which were given in lastmonth's article.The inductance of the choke coil is proportionalto the cross section area of the core, to the squareof the number of turns of wire, and inversely tothe length of the air gap. This is expressed mathematicallyas:.(i)where L is the inductance in henries, A the netarea of the core cross section in square inches, Nthe number of turns, and G the equivalent airgap in inches. The equivalent air gapis definedas the total reluctance of the core, including theactual air gap, reduced to an air gap of the samecross section^which will replace it. The value ofequivalent air gap to use in designing the chokeis uncertain. It is best figured from the formula:.Nlin which N is the number of turns of wire, Ithe current in amperes, and B the flux density inlines per square inch. The value of I beingpredetermined, adjust the number of turns so asto give a flux density of not more than about50,000 lines per square inch, with a reasonablevalue of G. This is relatively easy with small currents,but with the larger currents it isverydifficult to maintain reasonable flux density.The value of G increases with the size of thechoke, starting with about 0.03 inches as aminimum.To avoid the mathematical difficulties of usingthe above formulas, calculation charts have beendevised to replace them, formula No. Ibeingrepresented by Chart II and formula No. 1 byChart I.The first things to begin with in designing achoke coil are the inductance and the currentcapacity. A reasonable length of air gap is thendecided upon, and a flux density of about50,000 lines per square inch assumed to startwith. The number of turns can then be foundfrom formula No. 2 or Chart I, after which thesize of core may be figured from formula No. ior Chart II. Here itmay be found that eitherthe amount of copper or the size of the core isexcessive from the standpoint of economical andcompact design, in which case it may be neces-or a smallersary to try again with a larger air gapflux density, or both. Several trials are oftennecessary before a reasonable design is arrivedat. Then with these vital factors settled, thenext step is to choose the size of wire to handlethe current, just as was done with the transformer.Here again it is convenient to lay out a fullsizedrawing of the choke coil, to see just how itsproportions will work out. As with the transformer,a compact arrangement should bestriven for. Enameled wire is best for the choke,as the voltage difference per turn is small andthicker insulation would make the choke unnecessarilybulky. Allow for about iV of insulationbetween the winding and the core.Insulating papers between layers are seldomused with choke coils. If the layout looks unwieldywith allthe winding on one side of thecore, it may be split into two coils on oppositelegs. Although this requires less wire per turn,about 10 per cent, more turns should be addedto each coil to make up for the effect of leakageof flux between them. With the drawing completed,the length around the center line of thecore may be measured and the theoreticallength of air gap computed on the basis of 0.005inches per inch of core length, and comparedwith the value used in the design, to make surethat the latter was not assumed too small. Theamounts of wire and core material may beestimated in the same manner as with the transformer.The resistance of the choke coil is animportant factor, and, knowing the total lengthof wire and looking up its resistance per thousandfeet in the wire table, on page 277 of theAugust article, itmay be readily estimated.If the resistance proves greater than desirable,use a larger size of wire.The solution of a typical example shouldclear up any doubtful points remaining. Supposea 2o-henry choke coil is desired, capable ofcarrying 85 milliamperes of direct current.Where a choke is connected directly to the outputof a rectifier without previous filtering, themaximum value of the rectified alternating currentmay be as high as1.57 times the value ofthe direct current. Since both the alternatingand direct currents contribute to the flux in thecore, and only the direct current component hasbeen used in the formulas, it iscustomary toallow for the alternating current component bymodifying the value of flux density substitutedin the formulas. About 35,000 lines per squareinch will be satisfactory. Assume an equivalentair gap of about 0.05 inches. The number ofturns of wire to wind on the coil may be foundfrom Chart I. The key at the bottom of thechart shows which scales to connect together.Accordingly, draw a straight line from 0.085on the current scale to 3 5,000 on the flux densityscale. Through the point at which this line crossesthe index line, draw a second line from 0.05on the equivalent gap scale until it meets theturns scale, at 6500 turns in this case. Next,the size of core to use is obtained from Chart II.Draw a line from 20 on the inductance scale to0.05 on the equivalent gap scale. Through thepoint at which this line intersects the indexline, draw a second line from 6500 on the turnsscale until it meets the core area scale. Thispoint indicates a net area of 0.74 square inches,which isapproximately equivalent to a core "square.As mentioned before, the design is not sostraightforward for the larger currents. It isdifficult to arrive at a compact, economicaldesign, and frequentlyit isnecessary to makeseveral trials. Sometimes a faulty design willnot be evident from the plain figures, but willshow up when the full-size drawing is made.The only remedy is to try again.Having settled on the number of turns andarea of the core, the next step is the determinationof the wire size. This is done in exactly thesame manner as with the transformer. Thencomes the full-size layout, estimation ofmaterials, and resistance calculation. If theresistance proves excessive for the particular useto which the coil is to be put) choose a largersize of wire and make a new layout. The designisthen complete.CONSTRUCTION"IpHEpreparation of the core of the trans-* former or choke coil should be undertakenfirst.Several sources of the material are open tothe constructor. Oftentimes a junked poletransformer may be obtained for a small sumfrom the shops of the local power company orfrom a junk yard, the core of which may beremoved, cleaned with kerosene or alcohol, andcut down to the required size. For use in a Bsocket power-supply device, the core of a toy

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OCTOBER, 1927 TRANSFORMERS AND CHOKES FOR POWER-SUPPLY DEVICES 381thoroughly before assembling. ent arrangement is toIf the interleaving type of constructionBis used, the building upof the core may be expedited byjproviding some sort of square corneras a guide, such as a cigar boxwith two adjacent sides removed.Only three sides of the core shouldBbe assembled at first, alternatingthe layers as shown in Fig. i; thefourth side is to be put in pieceby piece after the coils have beenOdd LayersEven Layersslipped into place. The partiallycompleted core is carefully removedto a vise and-, Fourth clamped,leg toand thebe added legs that receive the coilspiece bound tightly with a layer of tape,by piece afterorwindings are heavy string, which mayinbe later unwound as the coils areplacepushed onto the core. The jointsshould be carefully trued up, makingsure that the pieces butt togetherwell. A wooden mallet, ora rawhide or lead hammerTransformer Coremay beused for this purpose.FIG. IPreparing the coils is not difficultif done properly. They shouldtransformer will often be found to be about the be evenly wound in layers, not only toright size without cutting. Ordinary stovepipe make for compactness, but to prevent theiron may be cut to size and used, but it will possibility of two turns of widely differentincrease the losses, resulting in excessive heating voltages coming together. Coils of small enameledand waste of power unless a much larger core iswire should have a layer of paper be-used. The use of regular transformer steel is tween each layer of wire, to keep the windingrecommended wherever possible. Motor or armatureeven and to improve the insulation. If specialrepair shops sometimes handle it.Supply insulating papers are not available, tracing paperhouses that cater to transmitting amateurs such as used by draftsmen, will serve the purposeoften stock it and will cut it to any desired size. nicely; ordinary wrapping paper can also beTheir advertisements may be found in current used. These papers may be omitted with theamateur periodicals or their addresses obtained larger sizes of enameled wire, since they arefrom a neighboring "ham." This source lacking, easier to wind evenly and the voltage differencepurchase the best available grade of soft sheet between layers is less. They may be dispensediron or steel from a local tin shop. It should be with entirely if cotton-covered wire is used.not more than 0.014" thick. It is best to cut the Windings of cotton-covered wire may bematerial to size with squaring shears, or to have a made moisture proof and more rigid by applyingtinsmith do it, as accurate work is essential. a thin coat of shellac to each layer as wound, andUnless the pieces are square and of uniform size, baking the finished coil to dry it out. Enameledpoor joints at the corners will be inevitable and wire cannot be treated in this way, however, asthe resulting small air gaps will increase the core the shellac may soften the enamel. Small coils oflosses due to reduction of effective area. All enameled wire may be made rigid by dippingrough edges should be removed and the pieces them in melted wax, such as a mixture of beeswaxshould lie flat.and rosin. Ordinary paraffin is not suitable, as itIf an old core is used, the construction of the may soften if the transformertransformer will of course depend upon whateverruns at all warm.conditions are encountered. But assuming that Large coils may be painted [)the raw material is available, several types of with insulating varnish orcore arrangement are possible. The one shown black asphaltum paint.in Fig. i, using interleaving joints, is most convenientfor transformers. Two different sizes of be made self-supporting orThe windings may eitherpieces are required, shown as A and B, with wound on a fibre spoolenough of each to stack twice as thick as the which is slipped over thecompleted core when tightly clamped. Another core. The former is theway of building up the core is indicated in Fig. 2, more common method. Abut this type is not practical unless the pieces square wooden mandrelof the core are very accurately cut and closely the same size as the corebutted together. This construction may be used cross section is first prepared,for choke coils, however, since an air gapis requiredcut to the samesomewhere in the core, its location beingimmaterial as long as the requisite total length islength that the winding isto be, and sanded smooth.provided. Fig. 3 illustrates a modified constructionFor the larger core sizes itfor chokes which has the advantage of beingeasier to clamp. In this case the pieces are cut tomay have to be built up ofseveral thicknesses of woodfour different sizes, with enough of each to make glued together. Flanges aup the full thickness of the core.quarter of an inch thickSome sort of insulation between the laminationsare then screwed to eachshould be provided, to reduce the core end, as shown in Fig. 4;losses due to eddy currents. Commercial transformerthese are later to be reingsteel usually comes with an oxide coatmovedin order that thefor this purpose. Ordinary rust is often winding may be slipped off.sufficient when the oxide coatingis not present, Some means of rotatingbut it is better to apply a thin coat of shellac winding form mustto one side of each piece, allowingit to dry be provided. A conveni-drive a spike in the center of one end of themandrel, grind or file off the head, and secure theend of the spike in the chuck of a hand or breastdrill which isclamped horizontally in a vise.A lathe may also be used. A small geared emerywheel is excellent for the purpose. Another commonmethod is to fasten the mandrel to a woodendisc which isclamped or wired to the flywheel ofa sewing machine. If a geared emery wheel orhand drill is used, the number of turns of wiremay be computed by determining the turns ratiobetween the crank and the spindle, and thencounting the turns of the crank. Another way isAllBBLayersFIG. 2to insert the spindle of a revolution counter into ahole in the free end of the mandrel, as shown inFig- 4-As the coils are to be taped when finished, winda layer of heavy string around the mandrel andfasten the ends. This is to be unraveled after thecoils are wound, enabling them to be slipped offeasily and allowing room for the tape. A layeror two of fibre is then cut to size and squarelyAir Gap-, r 1

382RADIO BROADCASTOCTOBER, 1927bent around the string-covered mandrel andglued in place. On high-voltage windings,above about 500 volts, add a few layers of empirecloth, which may be obtained at motor repairshops.THEWINDING THE COILcoil is now ready to be wound. Pass thefree end of the wire through a small holedrilled in the flange, leaving enough wire toprovide a lead to the panel. If fine wire is used,the lead and the first few turns should be of insulatedflexible wire, to avoid any possibility ofthe lead breaking off. The fine wire is thensoldered to this, carefully cleaned pf any excessflux, and the joint covered with a bit of tape.The rest of this first layer is then wound. If thewire is cotton-covered, this layer, and eachsucceeding layer as wound, may be given a thincoat of shellac as a binder, or insulating papersmay be used as described above, for enameledwire. The wire should be wound as tightly as itsstrength will permit. It may be necessary here towear a glove on the guiding hand, or to pass thewire over a piece of cloth held in the hand.Guiding the wire will be made easier if the hand isheld as far away from the coil as is convenient.The turns should be kept close together and notallowed to overlap, and extreme care should beexerted to avoid any possibility of shorted turns.A shorted turn acts as an independent shortcircuitedsecondary and will burn out as soonas the transformer is connected to the line.Where taps are brought out, the turns per layershould be so arranged, if possible, that the tapswill come at the end of a layer. Be especiallywatchful here for shorted turns. In finishingthe winding, pass the end of the wire throughanother small hole in the flange and fasten thelast few turns with a bit of sealing wax. Withfine wire the last few turns and the lead shouldbe of flexible wire just as at the start. If anotherwinding is to be placed over the first, they shouldbe separated by several layers of friction tape orempire cloth.Where a split secondary is used, the two coilsmay be wound side by side, each covering halfthe mandrel, rather than one on top of the other,to insure their having symmetrical characteristics.An end flange may be removed while afibre separator is slipped in place, and one sidefilled tightly with cloth strips while the other isbeing wound, to prevent the separator beingcrowded over. A split or center-tapped filamentwinding of only a few turns may be wound bymeans of a pair of wires, each comprising half ofthe total number of turns, the end of one wirebeing connected externally to the beginning ofthe other so as to put them in series. The connectionbetween the two is used as the centertapṪhe finishe d winding may be removed from theform by taking off .one of the flanges and pullingout the layer of string, after which the coil canbe slipped off. Itmay then be taped, as in Fig. 5,using ordinary friction tape and advancing halfthe width with each turn. High-voltage coilsshould he covered withempire cloth tape. Thetape should not be allowedto bunch at theinside corners, ortrouble will be experiencedin inserting thecore. The coils shouldnot be taped too heavily,or they will notcool well.Small coils of enameledwire may beChuckFlanged winding MandrelFIG. 4tape.conveniently made bywinding them onRevolution Counterspools made of piecesof fibre glued together.ing the core. Another method is to drill a holeAfter being wound thewire may be covered with a layer or two of in each corner of the core for a small bolt, but theheavy paper or one layer of frictiondiameter of the hole should not exceed onefifthof the width of the core leg, otherwise theThe finished coils, after painting or moistureproofing,may now be placed on the core, unwindingeffective area of the core will be reduced. A panelthe string on each leg as its coil is pushed of bakelite or hard rubber may be provided toon. The fourth leg of the core is then put in, piece hold the terminals, which may be ordinary bindingby piece, hammering the corners up tightly.posts or soldering clips. The leads may beIf the winding fits too loosely, extra core pieces brought up to the back of the panel and solderedmay be forced in, taking care not to damage the to the terminals. They should be kept wellinsulation of the coil, or small wooden wedges separated from each other and insulated withmay be driven between the coil and the core. "spaghetti" or similar tubing. Flexible insulatedhook-up wire makes good leads. The terminalsof the transformer should be plainly and permanently--Flexiblelabeled with their voltages.leadThe transformer should be tested before beingconnected to any other apparatus. First connectthe primary to the line without any loadon the secondary, to detect any shorted turns,which will show up as excessive heating or as anactual burn-out. If after several hours the transformeris only slightly warm, it is probably allright. The terminal voltages may be checkedwith an a. c. voltmeter, if desired.After the choke coil iscompleted the air gapmust be adjusted to the proper value. This canonly be done experimentally, by connecting thechoke to its associated apparatus and changingthe gap until the best filtering action is obtained.The gap should then be filled with cardboard or acloth pad and the core permanently clamped, toprevent the gap being gradually closed by themagnetic pull between the two parts of the core.The inductance of the choke cannot be measureddirectly. If the necessary meters are available,it may be found as follows. Connect the choke inseries with a battery and measure the voltageacross the coil and the current in amperesthrough"--Tape half-lappedmay then be calculatedfrom Ohm's Law:FIG. 5The whole assembly should be made rigid, to Then connect it across a source of a. c. voltagereduce any audible hum when the transformer of known frequency, such as the no-volt line,is in use.and again measure the current and voltage. TheMethods of mounting the transformer or chokecoil are shown in Fig. 6. Angle iron, strap iron, orimpedanceis then:square lengths of wood may be used for clamp-The inductance, L, may then be calculatedfrom the formula:Z= T/R2+(2icfL)2Or its equivalent:FIG. 6The writer wishes to acknowledge his indebtednessto Prof. F. S. Dellenbaugh, Jr., of theMassachusetts Institute of Technology, for thedesign formulas applying to the choke coil.

RADIO BROADCAST ADVERTISER 383'ONot a Super-HeterodyneNot Tuned Radio FrequencyNot RegenerativeAH models of the R. Q. S. "OCTA-MONIC" will be on display at the Radio World's Fair, New McdisonSquare Qarden, between the 19th & 24th of September inclusive at the booth of the R. Q. S. Mfg. Co., Inc.BUILT FOR MODBRN BROADCAST CONDITIONS

384 RADIO BROADCAST ADVERTISERNew aA. C. Tube ModelsR. G. S. "Octa-Monic"A-C Tube Kitincluding detailed instructions and graphicblue-prints; all necessary apparatus, power(A-C Tube) trans/ormer, four'Uiay linevoltage switch, carefully tested and selectedheavy duty wire, lamp socket connectionsand cable etc., etc., readv to build ,$114.60R. G. S. "Octa-Monic"A-C Tube ChassisCompletely assembled according to latestlaboratory methods, with instructions andblue-prints /or installation, ready to pluginyour lamp socket and operate, $129.60R. G. S. "Octa-Monic"A-C Tube Receiverhoused in an attractive, partitioned, walnuttable cabinet, $149.60NOTE: In A- C Tube Models of theR. G. S. "Octa-Monic", the performanceis practically as startlingly satisfactoryas the Battery models. Volume andselectivity are about the same; the TonalDuality is slightly better on strong localstations but on distant stations or stationsof wea\ signal strength, a slight hum isnoticeable.To all intents and purposes, elaborate experimentshave proved all A-C modelsof the new and revolutionary R. G. S."Octa-Monic" quite satisfactory.Price NoticeAbove prices do not include CunninghamA-C and Fewer Tubes nor the "B" BatteryEliminator. All A-C models twilloperate on any good eliminator. This,therefore permits the use of your own "B"Battery Eliminator. It goes without saying,of course, that B Batteries will alsoperform perfectly satisfactorily.utstandingContributionsThe fundamentally new R. G. S. "Octa-Monic" Receiver developed by DavidGrimes is one of the four great radio developments of the past 10 years. TheR. G. S. "Octa-Monic" principles are fully as important and represent as basica contribution to the Radio Art as did any of the discoveries of DeForest, Armstrong,Alexanderson, etc., etc.These new and revolutionary principles of tuning, or the radio frequency endof the R. G. S. "Octa-Monic", produce results not only superior but, theseprinciples of tuning place this Receiver far in advance of any receiver developedto date. The R. G. S. "Octa-Monic" is fundamental and is as radically new aswas the Super-Heterodyne.These highly efficient principles employed in the new R. G. S. "Octa-Monic"cover not only the tuning or radio frequency end of this receiver but they coverthe amplification end as well. The R. G. S. "Octa-Monic" amplifier (Powertube in the last stage,) gives, unquestionably, as perfect reproduction as it ispossible to buy, regardless of cost.The R. G. S. "Octa-Monic" comes to you more heavily endorsed by able authoritiesthan any other receiver ever presented to the Radio Public. The editorof one of the most important radio publications in America said that it was theonly receiver he had ever seen in his career as an editor to which the terms "newand revolutionary" could be applied in good faith.Selectivity superior to the super-heterodyne without cutting side bands. Selectivity enough toeliminate the heterodyne squeals of local stations, operating on a higher octave; selectivity that isequal over the whole dial without being at all critical at any point; selectivity enough to separatewith ease the local jumble of Metropolitan (New York City, Chicago, San Francisco, etc.) stations;selectivity enough to give five (5) degreesof silence between stations WEAF and WNYC in a location200 yards away from WNYC.Selectivity positive enough to make use of vernier control unnecessary.Sensitivity or Distance-Getting Ability. Can work right down to static level. This insurestrans-continental or trans-oceanic reception on favorable occasions.Volume sufficient to fill a hall that will seat 5500.Tonal Quality that is as nearly perfect as development in the Radio Art will permit.Straight Line Audio Amplification.Stability Margin of 800 ohms. The average receiver has a stability margin of from 6 toao ohms. This high stability margin of the R. G. S. "Octa-Monic" eliminates any possibilities ofhowling from poor batteries or "motor-boating" from eliminators. Batteries registering as low as10 volts will deliver a clear tone, free from howling, in this receiver.Straight Line Radio Amplification insuring reception at all broadcast wavelengths.Straight Line Volume Control that makes distorting of tone impossible.Automatic Wavetrap for prevention of heterodyning and whistling resulting from stationsoperating on one-half wave-length or on first octave beat.Automatic Filament Control.Employs 135 Volts or 180 Volts. Draws 22 mils.Each R. G. S. "Octa-Monic" is carefully tested with scientific apparatus and under actual broadcastingconditions before it leaves the laboratories; while every piece of apparatus is just as thoroughlytested before it is built into this receiver.The R. G. S. "Octa-Monic" is a closely co-ordinated Receiver built of quality apparatus. Carefultests are the basis for the choice of each piece of apparatus, tests that not only determine the meritsof each individual part, but more importantly its relation to the whole receiver.Standard Cunningham tubes (?CX joi-A's and iCX 371, Power tube in last stage) and WesternElectric Cone are recommended for best results.The R. G. S. "Octa-Monic" is highly attractive in appearance. It is built on five-ply, speciallyshellaced sub-panel (oo| x 9!) to which is mounted beautifully designed panel, walnut finished,7 x n. The panel and dials are trimmed in gold.The R. G. S. "Octa-Monic" is unusually simple to construct. The instructions and blueprintsare more comprehensive and complete than any issued to date. They are

RADIO BROADCAST ADVERTISER 385ffQCTA-MONICof Ten Years of Radio Developmentto operate. There are but two dials, the nearest possible approach to tuning efficiency, and you willfind that stations actually "click" or "tumble-in" for you as you slowly rotate your dials.The customary need of wooden screw-drivers or involved balancing devices is entirely removedin the R. G. S. "Octa-Monic." Major or minor adjustments are unnecessary. The R. G. S. "Octaandas a conse-Monic" is free from ordinary service. Tuning condensers are the only moving parts,quence, there are no fussy mechanisms, either mechanical or electrical, to get out of order.The R. G. S. "Octa-Monic" operates satisfactorily on either a good "B" battery eliminator orbatteries without "motor-boating" or howling.The R. G. S. "Octa-Monic" is so designed that it will fit any good cabinet or console. Write forcabinet and console literature.Orders cannot be accepted for individual pieces of apparatus or blueprints.The R. G. S. "Octa-Monic" is sold as follows: i. R. G. S. "Octa-Monic" kit of parts includingall required apparatus, transformers, rheostats, drilled and engraved aluminum panel, etc. even thenecessary Acme Celatsite wire is enclosed in the attractive container, complete instructions andblueprints, ready to build, $79.60 2. R. G. S. "Octa-Monic" chassis, completely assembled accordingto latest laboratory methods with complete thorough operational instructions, ready to operate,$89.60, 3. R. G. S. "Octa-Monic" Receiver housed in an attractive, well-designed, walnuttable cabinet, $104.60, 4. R. G. S. "Octa-Monic" Tuning kit, including all necessary apparatusand complete blue-prints and instructions on how to build the radio frequency end of this Receiverand on how to hook-up to your favorite amplifier, $59.60 5. R. G. S. "Octa-Monic" TuningChassis, completely assembled according to latest laboratory methods with complete instructionsand ready to wire to your amplifier, $66.60.All models of the R. G. S. "Octa-Monic" have been adapted to the CunninghamA-C and Power Tubes (Four (4) CX 326, one (1) C 327, and one (1) CX 371.The "B" Battery Eliminator and the Cunningham Tubes are not included inthe following prices. This eliminates an unnecessary expenditure on your partbecause the A-C Tube models of the R. G. S. "Octa-Monic" have been designedto operate satisfactorily with any good "B" Eliminator. It is recommended ifyour "B" Eliminator has no "C" battery tap, that you use the regular 40 voltsof C battery.The A-C Tube models are sold as follows (i) The R. G. S. "Octa-Monic" A-C Tube kit, ineludingall necessary apparatus with complete and thorough blue-prints, and instructions, ready tobuild, $114.60 (2) The R. G. S. "Octa-Monic" A-C Tube Chassis, completely assembled accordingto latest laboratory methods, with thorough operational blue-prints and instructions, ready toplug-in your light socket and operate, $129.60 (3) The R. G. S. "Octa-Monic" A-C Tube Receiverhoused in an attractive, well-designed, walnut table cabinet, $149.60The R. G. S. "Four" employing the Inverse Duplex System (i) R. G. S. "Four" Kit, all parts, completeinstructions, $74.40. (2) Chassis, assembled according to latest laboratory methods, $84.40.All prices slightly higher west of Denver. Canadian and Export prices on request.Go to your dealer to-day and insist on a demonstration. If he hasn't stocked the R. G. S. "Octa-Monic" yet, tear off and mail to us the attached coupon with the required information. Every effortwill be made to arrange a demonstration for you.Arrange for that demonstration now because you have a real radio thrill waiting for you. In theR. G. S. "Octa-Monic" you will hear radio at its best. And when you hear the R. G. S. "Octa-Monic" you will know why "The it is: Synonym of Performance"All models of the R. G. S. "Octa-Monic" and the R. G. S. "Four" are fully protected byGrimes Patents issued and pending."Trade Mar^ Registered.DEALERS: Write for Complete Merchandizing PlansR-G'S Manfg. Co.,of theInc.Grimes Radio Engineering Company, Inc.Staten IslandNew YorkBattery or "B" EliminatorModelsR. G. S. "Octa-Monic" Kitof parts including all required apparatus,transformers, rheostat, drilled and engravedpanel, etc., etc., even the necessaryAcme Celatsite unre is enclosed in the attractivecontainer; complete and thoroughinstructions and blue-prints, ready tobuild, $79.60.R. G. S. "Octa-Monic" Chasiscompletely assembled according to latestlaboratory methods, ready to operate,$89.60R. G. S. "Octa-Monic" Receiverhoused in an attractive, well-designed.u'alnuttable cabinet, $104.60R. G. S. "Octa-Monic"Tuning Kitincluding all necessary apparatus and completeblue-prints and instructions on howto build the radio frequency end of this receiverand on how to hooff up to your favoriteamplifier, $59.60R. G. S. "Octa-Monic"Tuning Chasiscompletely assembled according to latestlaboratory methods with complete instructionsand ready to urire to your amplifier,$66.60R. G. S. MANFG. CO., Inc.Staten Inland, New YorkGentlemen:I want to hear your R. G. S. "Octa-Monic." Please arrange withmy dealer, whose address I have printed below, for a demonstration.I am much interested in this receiver but this request fora demonstration and literature, you understand, entails no obligationon my part.My NameStreetCity or StateMy Dealer's Name .His AddressBUILT FOR A\ODERM BROADCAST CONDITIONS

386 RADIO BROADCAST ADVERTISERTirelessPerformanceThese gulls fly and fly until we wonder how such staminacan be contained in so frail an object.Just so with CeCo Tubes. A strong combination of frailmaterials. Glass for- a covering; hair-like wires for filament;fine spun metal for grid.But so carefully engineered, so cleverly assembled so skillfullyexhausted, so thoroughly tested that their durabilityis astounding to the radio operator and fan who judgesCeCo performance by ordinary standards.You expect MORE of CeCo Tubes and get more.A Type for Every Radio NeedGeneral Purpose Tubes, Special Purpose Tubes, PowerTubes, Filament Type Rectifiers, Gas Filled Rectifiers andA. C. Tubes.Ask your radio dealer for completedata sheet of CeCo Tubes.C. E. MANUFACTURING CO., Inc., Providence, R. I.Announcing Our NewGas Filled Rectifier(NO FILAMENT)TYPE D-GMaximum Volts 300 Maximum Cur. 85 M-ALong Life without decrease in outputare not exceeded.is assured if these valuesEasy Filtration. Less strain on Filter condensers and smootheroutput with less Hum or Ripple.These tubes are tested in a Standard rectifying circuit using welldesigned parts. The unit is connected to a ripple test position,and tube checked both by phones and observed on an oscillograph,insuring a perfect tube which will give excellent results inwell designed and constructed units.Write for Data Sheet givingCharacteristics of all CeCo TubesPRICE $5.00Makes a Good "B" Eliminator BETTER

RADIO BROADCAST ADVERTISER 387RestoredEnchantmentThis is the kvereadyLayerbilt that givesyou Battery Power forthe longest time andthe least money.IHERE is no doubt of itradiois better with Battery Power.And never was radio so worthy of theperfection of reception that batteries,and batteries alone, make possible.Today more than ever you needwhat batteries give pure DC, DirectCurrent, electricity that flowssmoothly, quietly, noiselessly.Whensuch is the current that operatesyour receiver, you are unconsciousof its mechanism, for you do nothear it humming, buzzing, crackling.The enchantment of the program iscomplete.Batteries themselves have improved,as has radio. Today theyare so perfect, and so long-lasting,as to be equal to the demands of themodern receiver. Power your setwith the Eveready Layerbilt "B" BatteryNo. 486. This is the batterywhose unique, exclusive constructionmakes it last longer than any otherEveready. Could more be said? Inmost homes a set of Layerbilts lastsan entire season. This is the batterythat brings you Battery Power withall its advantages, conferring benefitsand enjoyments that are really tremendouswhen compared with thesmall cost and effort involved in replacementsat long intervals. Forthe best in radio, use the EvereadyLayerbilt.EVEKtADYidio Batteries--they last longerRadio is better with Battery PowerAt a turn of the dial a radio program comes to you. It is clear.It is true. It is natural. You thank the powers of nature that haveonce more brought quiet to the distant reaches of the radio-sweptair. You are grateful to the broadcasters whose programs werenever so enjoyable, so enchanting. You call down blessings uponthe authority that has allotted to each station itsproper place. And,if you are radio-wise, you will be thankful that you bought a newset of "B" batteries to make the most out of radio's newest andmost glorious season.NATIONAL CARBON CO., INC. Q] New York San FranciscoUnit of Union Carbide and Carbon CorporationTuesday night is Eveready Hour Night 8 P. M., Eastern Standard TimeWEAF A'eir York WGR BuffaloW J AR Providence WCAE PittsburghWKKI Huston WSAI CincinnatiMinneapolis WIIAS LouisvilleWDAF Kannu City WTAM Cleveland wcco('"""'"*I St. Paul WSR AtlantaWKI Philadelphia WWJ Detroit KSD St. Louis WSM HashvilleWMC MemphisWON Chicago WRC WashingtonWOC Davenport WGY SchenectadyPacific Coast Stations 9 P. M., Pacific Standard TimeKPO-KGO San FranciscoKFI-tos AngelesKFOA-KOMO-ScattteKCW-Portfandflow you heard the neu, Tic-tor record by the Eveready Hour Group -orchestranngen m andMiddleton's Down South Overture and Dvorak's Coin' II.,,,.,-:'

388 RADIO BROADCAST ADVERTISERThe Radio BroadcastSHEETSVariable ResistTo carry plenty of power and withstandhigh voltage this new unit providesoutstanding advantages. A single turnof the knob gives full resistance variation.Units are practically heat-proof,and will dissipate up to 20 wattsthrough the entire resistance, withoutdanger of burning out. Resistanceremains constant at any knob setting.Used as improvementover present controls,or add to the "B"eliminator that has novariable voltage. A50,000 ohm unit attachedto high voltageterminal, provides atap adjustable to anyvoltage. When replacing present controls,use 100,000 ohms for detectorand 50,000 ohms for intermediate voltage.Also 10,000 and 500,000 ohms.Each ........ $2.00HEA-V~V DUTVPotentiomeleRIdentical with above Re*sistor, plus a third terminal.Potentiometersprovide better voltageregulation for "B" Eliminatorsthan the twoterminaltype and areeconomical because no fixedresistors are needed. Have ample currentcarrying capacity for any "B" power circuit.Try this improved regulation on your Eliminator.Resistances up to 10,000 ohms all wirewound. 1,000, 3,000, 10,000, 25,000, 50,000,loo.ooo ohms, $2.00.WIRE WOUNDTHE RADIO BROADCAST Laboratory Information Sheets are a regular feature of thismagazine and have appeared since our June, 1926, issue. They cover a wide rangeof information of value to the experimenter and to the technical radio man. It is not ourpurpose always to include new information but to present concise and accurate facts inthe most convenient form. The sheets are arranged so that they may be cut from themagazine and preserved for constant reference, and we suggest that each sheet be cut outwith a razor blade and pasted on 4" x 6" filing cards, or in a notebook. The cards shouldbe arranged in numerical order. An index appears twice a year dealing with the sheetspublished during that year. The first index appeared on sheets Nos. 47 and 48, in November,1926. In July, an index to all sheets appearing since that time was printed.The June, October, November, and December, 1926, issues are out of print. A completeset of Sheets, Nos. I to 88, can be secured from the Circulation Department,Doubleday, Page & Company, Garden City, New York, for $ i.oo. Some readers haveasked what provision is made to rectify possible errors in these Sheets. In the unfortunateevent that any such errors do appear, a new Laboratory Sheet with the oldnumber will appear.THE EDITOR.No. 129 RADIO BROADCAST Laboratory Information SheetOctober, 1927HOW IT FUNCTIONSThe Type 874 Glow Tube/T HE X type 874 tube is a special voltage regulator* designed for use in B power units to maintainthe voltages, supplied by th^ unit, constant. Anordinary B power unit operated without a glow tubehas a comparatively poor regulation, i.e., the voltagechanges considerably with changes in theamount of current being drawn from the unit. Itwould obviously be of decided advantage if thisvoltage could be made to remain practically constantat all loads. The power unit could then be usedwith any receiver irrespectiveof the amount ofcurrent being drawn by it (within reason) with theknowledge that the actual voltages designated onthe binding posts of the B device were being supplied.How the glow tube functions to maintain thevoltage constant may be understood by referenceto the curve A. This curve is plotted by measuringthe voltage across the glow tube with various loadcurrents and it should be noted that the voltageacross the tube is practically 90 at all loads up tomore than 40 mA. In ordinary operation, whenthere is no current being drawn from the 90-volttap, the glow tube current is about 45 milliamperes.Then, if current is drawn for a receiver from the90-volt tap, which would ordinarily cause the voltageto go down, the current through the glow tubeautomatically decreases, providing for the currentrequired by the set. The voltage thereby is maintainedat exactlyCurve B 90.illustrates the curve of output voltagethat might be obtained from a B power unit notusing a glow tube. At no load the voltage is 123,while at a load of 10 mA. the voltage drops to 90-If, however, the receiver requires 20 milliamperes,the actual voltage available would be only 60 volts.10 20 30 40 50 60 70 80 90 1001, LOAD CURRENT IN mA.No. 130 RADIO BROADCAST Laboratory Information SheetOctober, 1927Built for the heavy currentof A 6? B powercircuits. The wire iswound over asbestos,fixed with heat-proof cement. Amplearea. Flat and thin, making them easyto mount. Resistance values for allABC Power Circuits.At your dealer's or C. O. D. Send for the newCentraiab A and B power circuit Literature.CENTRAL22 Keefe Ave.RADIOLABORATORIESMilwaukee, Wis.

RADIO BROADCAST ADVERTISER 389Dalkite has pioneered-but not at public expense,Balkite "AContains nobattery. Thesame asBalkite"AB' ' below, but forthe "A" circuit only. Not a batteryand charger but a perfected lightsocket "A" power supply. One ofthe most remarkable developmentsin the entire radio field.Price$32.50.Balkite "B'lifein radio.The accepted tried and provedlight socket "B" power supply.300,000 units in use show that itlasts longer than any device in radio.Three models: "B"-W, 67-90volts, $22.50; "B"-135,* 135 volts,$32.50; "B"-180, 180volts,$39.50.Balkite now costs no more thanthe ordinary "B" eliminator.Balkite ChargersStandard for "A" batteries. Noiseless.Can be used during reception.Prices drastically reduced. Model"J,"* rates 2.5 and .5 amperes, forboth rapid and trickle charging,$17.50. Model "N"* TrickleCharger, rate .5 and .8 amperes,$9.50. Model "K" Trickle Charger,$7.50.*SpeciaI models for 25-40 oclej atslightly higher prices.Prices are slightly higher West ofthe Rockies and in Canada,The great im-provements in radio n.powerby Balkite.*rom trouble seldom equalled in. i any industry. Because the firsthave been made isFirst noiseless battery charging,Then successful light socket "B"BalkiteltnB, ,, purchased ,5 years ago,stiU in use and will be for yearsto come. Because to your radiodealer Balkite is a synonym forquality. Because the electrolyticrectification developed and usedpower. Then trickle charging. And by Balkite is so reliable that totoday,most important of all, Bal-ing no battery in any form, supplyingboth "A" and "B" power directlyfrom the light socket, andoperating only while set is in use.This pioneering has beenimportant. Yet alone it wouldnever have made Balkite one ofthe best known names in radio.Balkite isleader becauseof Balkite performanceir*the hands ofitsowners.Because with2,000,000*units in thefieldhas aBalkiterecordof long lifeand freedomtoday the establishedBALKITE "ABContains no battery. A complete unit, replacing both"A" and "B" batteries and supplying "A" and "B"current directly from the light socket. Contains nobattery in any form. Operates only while the set isin use. Two models: "AB" 6-135,* 135 volts "B"current, $59.50: "AB" 6-180, 180 volts, $67.50.day it is standard on the signalkite"AB,"a complete unit containsystemsof most American as wellas European and Oriental railroads.Because Balkite ispermanentequipment. Balkite haspioneeredbut not at the expenseof the public.Today, whatever type of setyou own, whatever type of powerequipment you want, whateveryou want to pay for it,has it.BalkiteAndproduction isso enormousthatpricesare astonishinglylow.Your dealerwill recommendthe Balkiteequipmentyou needforFANSTEEL PRODUCTS COMPANY, Inc.sNprth Chicago, Illinoisru^_L_>Tttl_BalkiteTower Units-your set.

390 RADIO BROADCAST ADVERTISERW.W.V.-.W.VUnaffected by temperature.moisture or atmosphericchanges. Does not ageorchangein resistance.A solid-molded fixed resistor,baked under highpressure, and accuratelycalibrated. Can be solderedwithout affecting accuracy.Two RemarkableRadio ResistorsBradleyunit'A is an outstandingsuccess! It is a fixed resistor forradio circuits of all kinds, and hasa capacity of a watts. It isruggedand can be soldered easily, withoutaffecting the rating of the unit.Bradleyohni'E is widely used bymanufacturers ofB'Eliminators forplate voltage control. Its remarkablywide, noiseless range, accomplishedwith two columns ofgraphite discs, accounts for itstremendous popularity.Use Allen'Bradley resistors inyour own hook-ups for superlativeresults. Follow the example ofprominent radio manufacturers.They know!No. 131 RADIO BROADCAST Laboratory Information Sheet October, 1927ONDATA ON CONSTANTSLABORATORY Sheet No. 132 is given acircuit diagram of a resistance-coupled amplifierusing the new type 240 high-mu tube (Cunninghamtype 340). To obtain satisfactory operationfrom such an amplifier it is essential that severalpoints be given careful consideration. In the firstplace it is essential that excessive C bias is,not usedon any of the high-mu tubes. The following valuesshould be used in combination with the voltage shownin the circuit diagram to prevent overloading: 1 volton the first stage, 3 volts on the second stage, and40.5 volts on the 171 power tube. The second con-structedsideration of great importance in the constructionof such an amplifier is that the coupling condensers,Ci, Q, and Ca, be of the best quality that can beobtained. Even a small amount of leakage acrossthe condenser, due to faulty insulation, will permitsome of the plate potential to leak through it to thegrid of the next tube and this will not only causedistortion but very frequently will make the amplifierabsolutely inoperative. Use only the best ofmica condensers.It is, of course, also essential that the plate andgrid resistance be noiseless in operation but it is notnecessary that they be exactly of the values givenin the circuit. A variation of ten or twenty per cent,in these values is quite unimportant. The platesupply for the amplifier may either be a well con-Resistance-Coupled AmplifierB power unit or batteries. No trouble what-when operating thesoever should be experiencedunit from new batteries, but it is possible that"motor-boating" troubles will develop when theamplifier is used with some B power units. Theoverall gain is comparatively high and difficultiesof this sort become more pronounced as the amplifi-3 1000Bradleyohm-E is available in several rangesand ratings. Sold in distinctive checkeredcartons. Ask your dealer for Bradleyohm-EELECTRIC CONTROLLING APPARATUS

RADIO BROADCAST ADVERTISER 391Down BringsYou Either ofTheseGuaranteed EliminatorsSuper-Power"A" EliminatorHere is a constant, unvarying, smooth, hnmless currentat 6 volts for any radio receiver using 201 -A and powertubes. Uncertain storage batteries with their changingpower, chargers and other bothers are done away with.This eliminator completely replaces "A" batteries. Inaddition your set gets perfect current at all times it isalways ready to do its best. Stations come in easily andquickly.Not a Battery-ChargerCombinationThis Super-power "A" Eliminator consists of a largecapacity rectifier which changes the alternating houselightingcurrent into direct current. Then a highly efficientheavy duty filter system of extremely high capacitychanges the pulsating direct current from therectifier into smooth, even current for lighting the filamentsin the radio tubes. Anyone can install this Superpower"A"Eliminator in a few minutes. Just attach itto your set and plug it into an electric light socket.Your set is instantly supplied with the correct amountof hum-free current, used only when set is in use. Youare assured of good current whenever you want it. This"A" Eliminator works perfectly whether used once orIt has no moving parts tothousands of times a year.wear out. Operates from light socket 110-120 volts,60-60 cycle A.C., output 6 volts direct current for allsets up to 12 tubes with power tubes.There are no batteriesto be charged. It is fool-proof in operation. Onceattached it is permanent you can forget you everheard about "A" batteries.Test It for 30 Days BeforeJust fillYou Buyout the coupon below and mail it to us with adollar bill. We will send you this "A" Eliminator totest. It must deliver satisfaction before you buy. After30 days trial pay only $5.00 a month until you have paid$31.50. Only our great buying power enables us to makethis liberal offer and to also sell this Super-power "A"Eliminator for easily }| less than is ordinarily asked.Take advantage of this offer today.Remember if you are disappointedin any way we will refundyour dollar anday return postage.Y'ou run no risk. Ordernow.Super-Power"B" EliminatorDo away with "B"batteries their annoyance and theconstant expense of always getting new ones. The great"B"EIimintoroffered here replaces thempermanently.Just attach this eliminator to your set plug it into anelectric light socket and a steady flow of power is deliveredto your set. Hum, noise, distortion and all otherdisturbances are gone. Built with heavy duty chokes,transformers and the finest of condensers in the filtersystem, it is 100% efficient at all times the most modernand flexible"B"Eliminator in the world. Used withany good "A" Eliminator it completely electrifiesyour set.Complete With Raytheon TubeThis Super-power "B" Eliminator can be used withany set up to 12 tubes. It comes complete with fullwave rectifying 85 mil. Raytheon tube, making possiblethe delivery of great current at a high voltage. ThisRaytheon tube has indefinite life as it has no filamentto burn out. Delivers upto 180 volts.The case is beautifully finished in olive green Ducowith black panel etched in gold. Equipped with rubbercoveredcord and socket plug. High voltage taps andvariable adjustments enable the use of new power tubesOperates fromllO-120A.C., 60-60 cycle current. Has tapfor intermediate voltage on which 67^ to 90 voltsmay be obtained. The detector tap will supply 22'^ to67J4 volts. Variable adjuster will deliver any desireddetector voltage. On and off switch and high and lowvoltage switch are integral parts of the eliminator. Noadditional switches or cords are necessary.Only $1.OOWe make the same liberal offer on both the "B" and the"A" Eliminator. Fill out the coupon and mail it to uswith a dollar indicating which eliminator you wish. Ifboth are desired send $2.00. Each eliminator must thenmake good while you test it for 30 days before you payanother cent. After test the balance is due in easy installments.This "B"Eliminatoror dinarily sells for as high asthe cash price of $42.50. Thisis your opportunityto getit for only$29.50 payablein easyinstallments.Cotnpletelntractionswith eachunit (orwiringto set.Alail This Coupon.ELLIOTT RADIO CORPORATION, DEPT. 172709 West Lake Street, Chicago, IllinoisAttached find $1.00 for which you asree to send me ( ) "A" Eliminator at$31.50. ) (_"B" Eliminator at $29.50. (Send $2.00 if both are desired, as describedin your ad.) Full particulars will be sent me by return mail and mymoney refunded if I do not accept your offer.NameAddretsCityStatt,

392 RADIO BROADCAST ADVERTISERMorefor yourmoney in thisNo. 134 RADIO BROADCAST Laboratory Information SheetOctober, 192?THE EXPONENTIAL TYPEA CORRECTLY designed horn makes a verygood type of loud speaker. The best horn isone which radiates most uniformly over the requiredrange of frequency and it has been provedmathematically that the exponentially shaped hornconforms closely to this requirement. A horn is ofthe exponential type when its cross section areadoubles at equal intervals along its length. Forexample, a horn would be of the exponential typeif at the orifice it had an area of { square inchesand an area of \ square inches, 1 square inch, and2 square inches, at distances of 1, 2, and 3 feetrespectively from the orifice. The rate of expansiondetermines the lowest frequency of which the hornwill be a good sound producer. A horn which doublesin area every foot will reproduce down to about 64cycles, and a horn which expands twice as rapidlywill only reproduce well down to 128 cycles.A properly designed horn should be free fromLoud Speaker Hornsnoticeable resonance, and to prevent this the mouthof the horn should be made large enough to transmitthe sounds coming from it without any greatamount of back pressure. In the design of loudspeaker horns it has been found that, if the mouthis made comparable to \ of the wavelength correspondingto the low frequency cut-off point pf thehorn, the resonance in the horn will be negligible.The wavelength in feet is determined by dividingthe velocity of sound in feet per second, which is1 120, by the frequency. For example, a horn whosecut-off frequency is to be 32 cycles, correspondingto a wavelength of 39 feet, should have a mouth of39 divided by 4, or 9$ feet. These facts indicatedefinitely that a horn, to be a good one, must belarge. Small horns, whether they are or are notexponential, cannot radiate the low frequencies.The horn makes it possible for a comparativelysmall diaphragm to get a good grip on the air andthereby produce a large volume of sound. The smalldiaphragm and the large horn may be replaced bya large diaphragm, as is done in a cone type loudspeaker.The material of which the horn is made is important.Although a horn may be well designed,and constructed to the correct size, total length andexpansion per unit length, it may still fail to givereally good results because of resonant effects in thematerial used in the construction. The materialused should have no marked resonant frequencyunless it is very low, where it might help to increasethe low note radiation.No. 135 RADIO BROADCAST Laboratory Information SheetOctober, 1927-^^^ -*2850 is an amazinglylow price for this "B" BrwerUnit. Yet, inspite of price,Sterling quality is maintainedthroughoutFor efficiency, long life,in fact forpermanent operation, only thegenuine Raytheon BH rectifieris used. For convenience there'san "on" and "off switch.Current regulation? It's perfect!Amplifier and detector voltagesare variable. An additionalprimary control regulates allvoltages to suit large or small sets.No wonder the Sterling R-81is found today on thousands of3 to 8 tube sets, giving constant,dependable light socket service,Ask your dealer for a demonstrationof the Sterling R-81.THE STERLING MFG. Co.283 1-53 Prospect Ave. ' Cleveland, OhioThe Sterling Mfg.Co.'i 21-year reputationstands behindevery dealer whosells thcLtcrimg line.RESONANCE CURVESTF TWO circuits are coupled togetherby a con-A denser, as shown in the sketch, and they are bothadjusted so that they are tuned to slightly differentfrequencies, we will find that a resonance curve ofFREQUENCYthe combination has the form shown by the solidcurve. The resonance curve of either separate circuitalone would have the form indicated by the dottedClosely Coupled Circuitscurve. It is evident from the resultant curve that thecombination of these two circuits produces a resultantcharacteristic curve which is quite broad andflat on the top in comparison with the quite sharppeak of either circuit alone. This double peaked effectis a characteristic of closely coupled circuits andhas been used to some extent in radio receivers.An ordinary resonance circuit consisting of asingle coil and condenser has a comparatively sharpresonance curve and therefore frequencies slightlyabove or below the resonant frequency are notamplified as well as the latter and, therefore, thetuned circuit tends to cut down the amplification ofthe side bands of the incoming wave and this causessome loss of high frequencies. If a receiver is madeup, however, with two coupled circuits, such as wehave indicated, this cutting of the side bands willnot take place because the flat top of the resonancecurve can be made sufficiently broad so as to giveequal amplification over a band 10,000 cycles wideand therefore practically equal amplification can beobtained at all frequencies 5000 cycles above or belowthe carrier frequency. The circuit has not beenused in actual practice to any great extent becauseof the difficult tuning required and because of thecareful adjustments necessary.No. 136 RADIO BROADCAST Laboratory Information SheetOctober, 192?THEORY AND USES/HE T> use of power lines for the dissemination ot* intelligence is becoming increasingly commonthroughout the country. Large power companieshave in many cases installed radio equipment forinter-communication between various power plants;these radio- frequency signals are transmitted overthe power lines rather than through the air, and, inthis way less interference is encountered. The systemhas also been used in some communities inorder to make it possible to receive musical programsat home by connecting a suitable devicedirectly to the power socket.For commercial use, this system has certainadvantages, such as lack of interference, whichmake its use valuable, but it is unlikely that thesystem will ever replace broadcasting. The numberof different stations that can be "tuned-in" by asubscriber using the system is naturally limited,and this is a definite disadvantage.The system actually differs very little from thatof ordinary broadcasting, the major differencebeing that the power of the transmitter, insteadCarrier Telephonyof being radiated into the air by means of an antenna,is coupled directly to the power line. Thecoupling between the transmitter and the powerline is generally made through high-voltage couplingcondensers and special filter and protectivecircuits. At the receiving end an ordinary radioreceiver can be used to detect the signals. It alsomust, of course, be coupled in some way to thetransmission line. The system is generally operatedin duplex so that transmitting or receiving can beaccomplished at any of the various terminals of thesystem.In carrier telephony it has generally been foundbest to use carrier frequencies somewhat above50,000 cycles. For comparatively low radio frequencies,around 10,000 cycles, there is considerableloss in the various power transformers in the line,and at frequencies intermediate between about10,000 and 50,000 cycles there will very likely besharp resonance peaks causing excessive loss atparticular frequencies. Above 50,000 cycles anordinary transmission line is fairly satisfactoryas a transmitting medium.

RADIO BROADCAST ADVERTISER 393VARIABLE LINE VOLTAGE&AYTHEO*CONSTANT OUTPUTREGARDLESS OF LOADRaytheonVoltage Regulator TubeTT7XPERIENCE gained in seven years of ex-\-j haustive research, experiments and tests,have enabled the Raytheon Research Laboratoriesto produce a new and fundamentallyimproved Voltage Regulator Tube of markedcharacteristics.Raytheon Type R, when incorporated in theproper B Power circuits, maintains constant voltageon the 90 and lower voltage taps and greatlyimproves the voltage regulation on the 180 and135 volt taps, regardless of variations in eitherthe line voltage or load current. The variablevoltage controls can be thus eliminated and theconstruction of the unit simplified.Raytheon BH a125 milliampererectifying tube,becauseofitsconstantheavy dutyoutput, is especiallydesigned foruse in conjunctionwith the RaytheonType RRegulator Tubein light socketpower units.Furthermore, this new tube has a very pronouncedeffect in eliminating the last vestige ofripple from the output, and when connected toan amplifier will completely eliminate"motor-boating".A new feature the starting anode incorporatedin type R, maintains constantly a state ofionization in the tube to prevent any "goingout" regardless of the load fluctuation.RaytheonRaytheon, Type R, 90 volts, 60 milliamperes Price $4.00Raytheon A the compact efficient recti*ner, new in principle and construction.For A battery chargers and A batteryeliminator units.Type R, can be used in any powerunit circuit now on the market employing a glowtube with greatly improved results. Diagrams ofan approved Type R tube installation, in connectionwith the heavy duty Raytheon BHtube, can be had from the Raytheon ResearchLaboratories upon request.RAYTHEON MANUFACTURING COMPANYCAMBRIDGE, MASS.Raytheon BA a350 milliampererectifying tubefor complete batteryelimination.Watch for thenew ABC powerunits employingthis rectifier.V THE HEART OF RELIABLE RADIO POWER

RADIO BROADCAST ADVERTISERA Varied List of Books Pertaining toTransformer Builders for ' AMERICAN TRANSFORMER COMPANY.55. CAPACITY CONNECTOR Description72. PLATE SUPPLY SYSTEM A wiring diagram and lay-*Over Twenty-Six YearsRadio and AlliedSubjects Obtainable Free With the Accompanying Couponr> EADERS may obtain any of (be booklets listed below by us~**- ing the coupon printed on Page 396 Order by number only.\. FILAMENT CONTROL Problems of filament supply,voltage regulation, and effect on various circuits. RADIALLCOMPANY.2. HARD RUBBER PANELS Characteristics and propertiesof hard rubber as used in radio, with suggestions on tor. BREMER-TULLY MANUFACTURING COMPANY.lustrations. Primarilyhow to "work" it. B. F. GOODRICH RUBBER COMPANY.3. TRANSFORMERS A booklet giving data on input andoutput transformers. PACENT ELECTRIC COMPANY.RESISTANCE-COUPLED AMPLIFIERS A general discussionof resistance coupling with curves and circuit dia-and templates for4_.grams. COLE RADIO MANUFACTURING COMPANY.5. CARBORUNDUM IN RADIO A book giving pertinentdata on the crystal as used for detection, with hook-ups,and a section giving information on the use of resistors.THE CARBORUNDUM COMPANY.6. B-ELIMINATOR CONSTRUCTION Constructional data transformers of special design.on how to build. AMERICAN ELECTRIC COMPANY.TRANSFORMER AND CHOKE-COUPLED AMPLIFICA-7.TION Circuit diagrams and discussion. ALL-AMERICANRADIO CORPORATION.8. RESISTANCE UNITS A data sheet of resistance unitsand their application. WARD-LEONARD ELECTRIC COMPANY.9. VOLUME CONTROL A leaflet showing circuits fordistortionless control of volume. CENTRAL RADIO LABORA-TORIES.Type PF-281, $25.00 each10. VARIABLE RESISTANCE As used in various circuits. ing fullCENTRAL RADIO LABORATORIES.1 1. RESISTANCE COUPLING Resistors and their ap-AS IN audio to audio amplification, with circuit diagrams.transformers,S'ication EJUR PRODUCTS COMPANY.12. DISTORTION AND WHAT CAUSES IT Hook-ups ofAmerTran products standfirst in the power transformerresistance-coupled amplifiers with standard circuits. ALLEN- other pertinent data.BRADLEY COMPANY.15. B-EtlMINATOR AND POWER AMPLIFIER InStrUCtionsfor assembly andfield. They are up-to-date in design,operation using Raytheon tube.and GENERAL RADIO COMPANY.dependable.153. B-ELIMINATOR AND POWER AMPLIFIER Instructionsfor assembly and operation using an R. C. A. rectifier.GENERAL RADIO COMPANY.type rectifier. NATIONAL COMPANY, INCORPORATED.16. VARIABLE CONDENSERS A description of the functionsand characteristics of variable condensers with curvesand specifications for their application to complete receivers.ALLEN D. CARDWELL MANUFACTURING COMPANY.BAKELITE A description of various uses of bakelitein17.radio, its manufacture, and its properties. BAKELITE THE Q. R. S. Music COMPANY.CORPORATION.19. POWER SUPPLY A discussion on power supply withparticular reference to lamp-socket operation. Theoryand constructional data for building power supply devices.ACME APPARATUS COMPANY.ing tube, and has a 750 volt plate20. AUDIO AMPLIFICATION A booklet containing dataACCESSORIESon audio amplification together with hints for the constructor.ALL AMERICAN RADIO CORPORATION.winding which enables it to be21. HIGH-FREQUENCY DRIVER AND SHORT-WAVE WAVE- electricity with specialMETER Constructional data andused with a UX-28i or 2i6-B rectifyingaddition, there46. AUDIO-FREQUENCY CHOKES A pamphlet showing PANY.application. BURGESSBATTERY COMPANY.automatic switches, alarms, etc.are filament heating windings forpositions in the circuit where audio-frequency chokes maybe used. SAMSON ELECTRIC COMPANY.47. RADIO-FREQUENCY CHOKES Circuit diagramsthe new AC tubes. Therefore,lustrating the use of chokes to keep out radio-frequencythis single unit will convert ACcurrents from definite points. SAMSON ELECTRIC COMPANY.48. TRANSFORMER AND IMPEDANCE DATAhouse current into filament andTables^ivingthe mechanical and electrical characteristics of transformersand impedances, together with a short description of theiruse in the circuit. SAMSON ELECTRIC COMPANY.49. BYPASS CONDENSERS A description of the manufactureof bypass and filter condensers. LESLIE F. MUTERCOMPANY.MITTERSBURGESS BATTERY COMPANY.50. AUDIO MANUAL Fifty questions which are oftenasked regarding audio amplification, and their answers. 28. B BATTERY LIFEAMERTRAN SALES COMPANY, INCORPORATED.Battery51. SHORT-WAVE RECEIVER Constructional data on areceiver which, by the substitution of various coils, may bemade to tune from a frequency of 16,660 kc. (18 meters) toType H-67 Heater Transformer is1999 kc. (150 meters). SILVER-MARSHALL, INCORPORATED.52. AUDIOa new unit recommended for useQUALITY A booklet dealing with audio-frequencyamplification of variouswith the RCA UX-226 raw AC amplifierUY-227 detector56. VARIABLE CONDENSERS A bulletin giving ankinds and the applicationto well-known circuits. SILVER-MARSHALL, INCORPORATED.analysis of various condenserstube. It also has a third filamentwith their characteristics.GENERAL RADIO COMPANY.winding capable of 57. FILTER DATA Facts about thehandling two UXfilteringof directcurrent supplied by means of motor-generator outfits used171 tubes. In connection with the with transmitters. ELECTRIC SPECIALTY COMPANY.59. RESISTANCE COUPLING A booklet giving somenew AC tubes, type H-67 becomesgeneral information on the subject of radio and the applicationof resistors to a circuit. DAVEN RADIO CORPORATION.the power source for the filament and60. RESISTORS Ais therefore a real "A" pamphlet giving some technical databattery eliminator.This transformer sells forenergy; also data on the ordinary resistors used in resistance-on resistors which are capable of dissipating considerablecoupled amplification. THE CRESCENT RADIO SUPPLY$12.00.COMPANY.62. RADIO-FREQUENCY AMPLIFICATION Constructionaldetails of a five-tube receiver using a special design of rad o-frequency transformer. CAMFIEI.D RADIO MFG. COMPANY.AMERICAN TRANSFORMER CO.63. FIVE-TUBE RECEIVER Constructional data onbuilding a receiver. AERO PRODUCTS, INCORPORATED.64. AMPLIFICATION WITHOUT DISTORTION Data and what dry cell battery tocurves illustrating the use of various methods applicationof amplification.with wiring diagrams. NATIONAL CARBON COMPANY.ACME APPARATUS COMPANY.66. SupER-H ETERODYN E Constructional details of aWe also make Audio Transformersseven-tube set. G. C. EVANS COMPANY.Choke Coils and Resistors.70. IMPROVING THE AUDIO AMPLIFIER Data on thecharacteristics of audio transformers, with a circuit diagram vacuum type of arrester.showing where chokes, resistors, and condensers can be used. COMPANY.New Transformersfor A.C. Power SupplyThe AmerTran Power TransformerType PF-28r, illustrated above,becomes virtually an A-B-C eliminatorwhen used with AC tubesand the proper filter circuit forDC voltages of from 425 to 650volts, plate current no milliamperes.This unit is designed foruse with the new UX-28i rectify-plate current, and grid bias potential.Used with types 709 and 854AmerChokes in the filter circuit, areceiver may be constructed tooperate entirely from the houselighting circuit.Write for Booklet, "Improving the AudioAmplifier," and data on Power Supply Unitt.178 Emmet Street Newark, N. J.out plan for a plate supply system to be used with a poweramplifier. Complete directions for wiring are given. AMER-TRAN SALES COMPANY.80. FIVE-TUBE RECEIVER Data are given for the constructionof a five-tube tuned radio-frequency receiver.Complete instructions, list of parts, circuit diagram, andtemplate are given. ALL-AMERICAN RADIO CORPORATION.81. BETTER TUNING A booklet giving much general informationon the subject of radio reception with specific il-for the non-technical home construc-82. SIX-TUBE RECEIVER A booklet containing photographs,instructions, and diagrams for building a six-tubeshielded receiver. SILVER-MARSHALL, INCORPORATED.83. SOCKET POWER DEVICE A list of parts, diagrams,the construction and assembly of socketpower devices. J EFFERSON ELECTRIC MANUFACTURING COM-PANY.84. FIVE-TUBE EQUAMATIC Panel layout, circuit diagrams,and instructions for building a five-tube receiver, togetherwith data on the operation of tuned radio-frequencyKARAS ELECTRIC COMPANY.85. FILTER Data on a high-capacity electrolytic condenserused in filter circuits in connection with A socketpower supply units, are given in a pamphlet. THE ABOXCOMPANY.86. SHORT-WAVE RECEIVER A booklet containing dataon a short-wave receiver as constructed for experimentalpurposes. THE ALLEN D. CARDWELL MANUFACTURINGCORPORATION.88. SUPER-HETERODYNE CONSTRUCTION A booklet giv-instructions, together with a blue print and necessarydata, for building an eight-tube receiver. THE GEORGE W.WALKER COMPANY.89. SHORT-WAVE TRANSMITTER Data and blue printsare given on the construction of a short-wave transmitter,together with operating instructions, methods of keying, andRADIO ENGINEERING LABORATORIES.oo. IMPEDANCE AMPLIFICATION The theory and practiceof a special type of dual-impedance audio amplification aregiven. AI.DEN MANUFACTURING COMPANY.93. B-SOCKET POWER A booklet giving constructionaldetails of a socket-power device using either the BH or 31394. POWER AMPLIFIER Constructional data and wiringdiagrams of a power amplifier combined with a B-supplyunit are given. NATIONAL COMPANY, INCORPORATED.ipo. A, B, AND C SOCKET-POWER SUPPLY A bookletgiving data on the construction and operation of a socketpowersupply using the new high-current rectifier tube.101. USING CHOKES A folder with circuit diagrams ofthe more popular circuits showing wher^ choke coils maybe placed to produce better results. SAMSON ELECTRICCOMPANY.22. A PRIMER OF ELECTRICITY Fundamentals ofreference to the application of drycells to radio and other uses. Constructional data on buzzers,NATIONAL CARBON COM-23. AUTOMATIC RELAY CONNECTIONS A data sheetshowing how a relay may be used to control A and B circuits.YAXLEY MANUFACTURING COMPANY.25. ELECTROLYTIC RECTIFIER Technical data on a newtype of rectifier with operating curves. KODEL RADIOCORPORATION.26. DRY CELLS FOR TRANSMITTERS Actual testsgiven, well illustrated with curves showing exactly whatmay be expected of this type of B power. BURGESS BATTERYCOMPANY.27. DRY-CELL BATTERY CAPACITIES FOR RADIO TRANS-Characteristic curves and data on discharge tests.life curves with generalcurves on tube characteristics. BURGESS BATTERY COM-PANY.29. How TO MAKE YOUR SET WORK BETTER A nontechnicaldiscussion of general radio subjects with hints onhow reception may be bettered by using the right tubes.UNITED RADIO AND ELECTRIC CORPORATION.30. TUBE CHARACTERISTICS A data sheet giving constantsof tubes. C. E. MANUFACTURING COMPANY.31. FUNCTIONS OF THE LOUD SPEAKER A short, nontechnicalgeneral article on loud speakers. AMPLION COR-PORATION OF AMERICA.32. METERS FOR RADIO A catalogue of meters used inradio, with connecting diagrams. BURTON-ROGERS COM-PANY.33. SWITCHBOARD AND PORTABLE METERS A bookletgiving dimensions, specifications, and shunts used withvarious meters. BURTON-ROGERS COMPANY.34. COST OF B BATTERIES An interesting discussionof the relative merits of various sources of B supply, HART-FORD BATTERY MANUFACTURING COMPANY.35. STORAGE BATTERY OPERATION An illustratedbooklet on the care and operation of the storage battery.GENERAL LEAD BATTERIES COMPANY.36. CHARGING A AND B BATTERIES Vaiious ways ofconnecting up batteries for charging purposes. WESTING-HOUSE UNION BATTERY COMPANY.37. CHOOSING THE RIGHT RADIO BATTERY Advice onto radio,53. TUBE REACTIVATOR Information on the care ofvacuum tubes, with notes on how and when thev should bereactivated. THE STERLING MANUFACTURING COMPANY.54. ARRESTERS Mechanical details and principlesof theNATIONAL ELECTRIC SPECIALTYof a new devicefor connecting up the various parts of a receiving set, andat the same time providing bypass condensers between theleads. KURF-KASCH COMPANY.(Continued on page $96)

'RADIO BROADCAST ADVERTISER 395VITROHM RESISTORS and RHEOSTATScover every resistance requirement incurrent supplyunit circuitsCHOOSE to build the power circuit you will this year and thereis a dependable Vitrohm Resistor and Rheostat exactly engineeredto meet your requirements.Resistance is the heart of power circuits. Assure yourself of quiet,permanent, and unfailing service by insisting upon Vitrohms forradio. Each of the 95 Vitrohm Radio Resistors and Rheostats iscircuit whereguaranteed unconditionally for continuous duty in any it operates within its watts-dissipation rating. And Vitrohms havethe highest watts-dissipation rating without resistance change ofall resistance units.The Adjustatis a new Vitrohm Rheostatdesigned for use in radio current supplyunit circuits.Each Adjustat has 15 steps of resistanceand is arranged for potentiometer connection.Its compact size, 2% inches in diameter,permits the use of several Adjustatsin circuits where adjustable resistance isdesirable.The AdjustatLike all Vitrohm Products, the resistiveelement, wire having a low temperaturecoefficient of resistivity, is embedded andpermanently protected by a fuse-on coatingof vitreous enamel.11 Types are available as listed below.The Adjustat is priced at $3.00.507-79, 1 ohm, 4 amp. 507-71, 2 ohms, 3 amp. 507-72, 6 ohms, 1.5 amp. 507-73, 20 ohms, 1.0 amp.507-74,^30 ohms, 0.75 amp. 507-80, 50 ohms, 650 m.a. 507-81, 600 ohms, 180 m.a. 507-75, 1000 ohms, 125 m.a.|j507-76, 225O ohms, 90 m.a. 507-77, 10,000 ohms, 40 m.a. 507-78, 25,000 ohms, 10 m.a.Raytheon and QRS ABC UnitsThree new Vitrolim Radio Products are immediately availabletor use in the Raytheon 350 m. a. and QRS 400 m. a.VitrohmABC Current Supply Units. Vitrohm Resistor 507-62,priced at $7.50, is tapped tor all voltages needed in the QRSCircuits.Vitrohm Resistor 507-70, priced at $7.50, is officially approvedby the Raytheon Laboratories for use with theirrectifier. (Illustrated.)Vitrohm Rheostat 507-59, priced at $5.50, is designed forseries primary control in both circuits.Grid Leaks for Transmitting CircuitsVitrohm Transmitting Grid Leaks are now available for theR.C.A. UX 852 and De Forest P and H transmitting tubes.Ward Leonard has developed a complete standard line oftransmitting grid leaks and rheostats covering all circuitsup to and including those of 1,000 watts input. If you areinterested in this and other radio apparatus, write for RadioBulletin 507 (1927-1928).It will be sent witaout charge.Ward Leonard/rectric Company31-41 SOUTH STREET ^^^X^ MOUNT VERNON, N. Y.resistor specialists for more than 35 years

396 RADIO BROADCAST ADVERTISERttftAPPROVED RADIO PRODUCTSModernize your radio set constructionwith these two great Yaxleycontributions to convenience, efficiencyand good appearance;AutomaticPower ControlA new and betterpower control thatcuts in the B eliminatorand cuts outthe trickle chargerwhen the set isswitched on. Cutsout the B eliminatorand cuts in thetrickle chargeriwhen the set is"switched off, automatically,unfailingly.No. 444 SeriesType. With the exclusively Yaxleyfeature that kaeps the voltage dropless than two-tenths (2-10) volts whenused with sets having a current drawequivalent to four 199 type tubes upto eleven 201 type tubes $5.00Cable ConnectorPlugPreserve the neat appearance of yourset by centering all battery wires inone neat, compact cable. Safe, simpleand sure. Plug is of handsome Bakeliteconstruction. Contact springs ofphosphor bronze. Positive contact.No. 660 Cable Connector Plug,Complete $3.00No. 670 Cable Connector Plug forBinding Post Connections, Complete $3.50At your dealer's.If he cannot supplyyou, send his name with your order toYAXLEY MFG. CO.Dept. B-9 So. Clinton StreetCHICAGO, ILL.68. CHEMICAL RECTIFIER Details of assembly, withwiring diagrams, showing how to use a chemical rectifier forcharging batteries. CLEVELAND ENGINEERING LABORA-TORIES COMPANY.69. VACUUM TUBES A booklet giving the characteristicsof the various tube types with a short description ofwhere they may be used in the circuit. RADIO CORPORA-TION OF AMERICA.77. TUBES A booklet for the beginner who is interestedin vacuum tubes. A non-technical consideration of thevarious elements in the tube as well as their position in thereceiver. CLEARTRON VACUUM TUBE COMPANY.87. TUBE TESTER A complete description of how tobuild and how to operate a tube tester. BURTON-ROGERSCOMPANY.91. VACUUM TUBES A booklet giving the characteristicsand uses of various types of tubes. This booklet may beobtained in English, Spanish, or Portuguese. DftFoMBTRADIO COMPANY.92. RESISTORS FOR A. C. OPERATED RECEIVERS Abooklet giving circuit suggestions for building a. c. operatedreceivers, together with a diagram of the circuit used withthe new 4OO-mill ampere r ctifier tube. CARTER RADIOCOMPANY.97. HIGH-RESISTANCE VOLTMETERS A folder giving informationon how to use a high-resistance voltmet r,special consideration being g'ven the voltage measurementof socket-power d- vices. WESTINGHOUSE ELECTRIC &MANUFACTURING COMPANY.102. RADIO POWER BULLETINS Circuit diagrams, theoryconstants, and trouble-shooting hints for units employing thBH or B rectifier tubes. RAYTHEON MANUFACTURINGCOMPANY.103. A. C. TUBES The design and operating characteristics of a new a. c. tube. Five circuit diagramsto Convert well-known circuits. SOVREIGN ELECTRICshow how&MANUFACTURING COMPANY.MISCELLANEOUS38. LOG SHEET A list of broadcasting stations withcolumns for marking down dial settings. U. S. L. RADIO,INCORPORATED.41. BABY RADIO TRANSMITTER OF 9XH-9EK Descriptionand circuit diagrams of dry-cell operated transmitter.BURGESS BATTERY COMPANY.42. ARCTIC RADIO EQUIPMENT Description and circuitdetails of short-wave receiver and transmitter used in'Arctic exploration. BURGESS BATTERY COMPANY.43. SHORT-WAVE RECEIVER OF 9XH-9EK Completedirections for assembly and operation of the receiver.BURGESS BATTERY COMPANY.44. ALUMINUM FOR RADIO A booklet containing muchradio information with hook-ups of basic circuits, withinductance-capacity tables and other pertinent data.ALUMINUM COMPANY OF AMERICA.45. SHIELDING A discussion of the application ofshielding in radio circuits with special data on aluminumshields. ALUMINUM COMPANY OF AMERICA.58. How TO SELECT A RECEIVER A commonsensebooklet describing what a radio set is, and what you shouldexpect from it, in language that any one can understand.DAY-FAN ELECTRIC COMPANY.67. WEATHER FOR RADIO A very interesting bookleton the relationship between weather and radio reception,with maps and data on forecasting the probable results.TAYLOR INSTRUMENT COMPANIES.73. RADIO SIMPLIFIED A non-technical booklet givingpertinent data on various radio subjects. Of especial interestto the beginner and set owner. CROSLEY RADIO COR-PORATION.74. THE EXPERIMENTER A monthly publication whichgives technical facts, valuable tables, and pertinent informationon various radio subjects. Interesting to the experimenterand to the technical radio man. GENERAL RADIOCOMPANY.75. FOR THE LisTENER-^-General suggestions for theselecting, and the care of radio receivers. VALLEY ELECTRICCOMPANY.76. RADIO INSTRUMENTS A description of variousmeters used in radio and electrical circuits together with ashort discussion of their uses. JEWELL ELECTRICAL IN-STRUMENT COMPANY.78. ELECTRICAL TROUBLES A pamphlet describingthe use of electrical testing instruments in automotive workcombined with a description of the cadmium test for storagebatteries. Of interest to the owner of storage batteries.BURTON ROGERS COMPANY.95. RESISTANCE DATA Successive bulletins regardingthe use of resistors in various parts of the rad'o circuit.INTERNATIONAL RESISTANCE COMPANY.96. VACUUM TUBE TESTING A booklet giving pertinentdata on how to test vacuum tubes with special reference toa tube testing unit. JEWELL ELECTRICAL INSTRUMENTCOMPANY.98. COPPER SHIELDING A booklet giving information onthe use of shielding in radio receivers, with notes anddiagrams showing how it may be applied practi:ally. Ofspecial interest to the home constructor. THE COPPER ANDBRASS RESEARCH ASSOCIATION.99. RADIO CONVENIENCE OUTLETS A folder givingdiagrams and specifications for installing loud speakers invarious locations at some distanc: from the receiving set.YAXLEY MANUFACTURING COMPANY.USE THIS BOOKLET COUPONU \nio BROADCAST SERVICE DEPARTMENTRADIO BROADCAST, Garden City, N. Y.Please send me (at no expense) th following book- |

RADIO BROADCAST ADVERTISER 397TJSF KARAS PARTSFOR THE FINEST^OJJf JVnrVTU} .r/AJVIO POSSIBLE RESULTSin building your 2-Dial Karas Equamatic orin building any other high grade receiverPRODUCTSThe NEW Karas Type 28Audio TransformerPrice, ?8.0OThe NEW Karas OutputFilter, Price ?8.0OThe NEW Karas S.F.L.Condenser with RemovableShaft, Price: .O0025 mfd.,5; .O0037 mfd. 5.25;.0005 mfd. 5.50)U must, of course, use Karas Parts when you build your NEW Karas 2-Dial Equamatic Receiver thepowerful 5-tube completely balanced and perfectly neutralized radio frequency circuit with which Karasscores again in another sensational success for 1927-28. This new receiver was designed by Karas engineersto operate at maximum efficiency with Karas parts and will only do so when these parts are used exactly asspecified. But ALL Karas parts are adapted for use in scores of other popular circuits are specified in the leadingsuccesses of 1927-28 by many leading radio publications and to get the maximum of efficiency the finestpossible results you should be sure to use Karas pajrts when building ANY receiver. There is not a circuit inpopular use which cannot be vastly improved through the use of these parts in place of less efficient ones.Karas EngineeringisKnown All Over the WorldAll over the world, wherever radio has penetrated, Karas parts are known for their precise, careful engineering.The reputation of the entire Karas line has been built upon sound radio engineering practice, allied with precisionmanufacturing methods, insuring positively and certainly that each Karas part will do exactly what we claim itwill do. Other manufacturers do not bother to work within limits of accuracy as close as those established in theKaras factories. Yet we know of no other way to build radio apparatus and have it exactly right. Our standardsare high, but they are essential to best results in radio performance. Sound engineering practice, scientific studyof every problem presented, and the finding of the correct solution, are Karas essentials upon which we have builtthe remarkable reputation Karas Products enjoy. For example, in our new Type 28 Transformers we use hermeticallyspun-sealed steel clad cases in which the impregnated windings are sealed. Moisture cannot enter thiscase, nor can the insulating compound ever get out. Thus the delicate windings are forever protected from injury.In our new S. F. L. Condensers we work within such close limits that the shafts of any Karas Condenser maybe instantly removed and interchanged with the shaft of any other Karas Condenser of the same type. In theKaras Micrometrie Vernier Dial we obtain a 63 to I gear ratio and you obtain i|ioooth of an inch tuning asa result. You will discover for yourself many other examples of Karas engineering as you use Karas parts in buildingyour sets.Use these Karas Parts for the 2-Dial EquamaticYou will wish to build a Karas 2-Dial Equamatic right away when you know how marvelouslysimple it is to operate how powerful and sweet-toned it is and what selectivityand volume it possesses. There is nothing else to equal it in a 5-tube receiver many 6 and7 tube sets cannot rival the 2-Dial Equamatic.This new Karas receiver is extremely easy to build. Our Complete, detailed instructionsmake every step very clear and very easy to follow. You can build this receiver in a fewhours and thus have one of the finest, most selective radio frequency sets you have everowned. To build this receiver you will need, in addition to certain standard parts easilyobtainable anywhere, the following Karas parts which your dealer has in stock for you:3 Karas Equamatic R.F. Transformers, each $4 $12.003 Karas Equamatic Type 17 Removable Shaft S. F. L. Variable Condensers, each $5.25 15.752 Karas Micrometric Vernier Dials, each $3.50 7.002 Karas Type 28 Impregnated Audio Transformers, each $8.00 16.00I Karas Output Filter 8.003 Karas Subpanel Brackets, set of 3 70I Karas 2-Dial Control System, complete with three extra shafts andall necessary assembly hardware for set 3.00Mail the coupon to-day for complete list of parts, and full information aboutthis receiver. Then order the necessary Karas and other parts from your dealerso you can build this set without delay. You will be delighted with it -willfind it a receiver of tremendous power, volume and tone, and the most satisfactoryreceiver you ever built. Be sure to mail coupon to us to-day.oAddressKARAS ELECTRIC CO.4033-J North Rockwell Street ChicagoKaras MicrometricVernier Dials,Price 3.50Karas Equamatic InductanceCoils, Set of 3, #12.0OKARAS ELECTRIC CO.4033 J North Rockwell St.ChicagoPlease send me complete dataon the new 2-Dial Karas EquamaticReceiver, and also data onthe Knickerbocker 4, as well asinformation about the new Karasparts.Name .AddressCity . . .State . .

398 RADIO BROADCAST ADVERTISERMfr fc-6 wr__ P - K (jt+ PI sin ut + (Ji sin j wt + ft sn'+ K &,' sin 1 wt -f KB; si*3 ut + KI%ftf'Sf/foYOU can't get away from "variables"in the radio power unit. Line voltagefluctuations, changes in receivertubes, differences in rectifier tubes, loweredrectifier output with age, unequaldrain for different yet inter-related circuitswell, there are many "variables"present and for which you must compensatewith suitable resistance values.Of course, if you are an expert mathematicianand engineer, preferring towork the slide rule than to enjoy radioprograms, then by all means get the funout of figuring the necessary resistancevalues. And don't forget to change theresistors from time to time to compensatefor the changing conditions.But if you are just the average radio enthusiast,seeking the best results withthe least troubles, then use variable resistorsto take care of all "variables."And when you say variable resistorthat means.iCLAROSTATCAVTION! Clarostat is being imitatedLook for the name stamped on the shell!GET THE FACTS!Ask your local dealer regarding Clarpstatsand how you can apply them inthat new or old radio power unit. Betterstill, send a quarter for our big 32-pagebook "The Gateway to Better Radio,"which contains a vast fund of informationon radio in general.AMERICAN MECHANICALLABORATORIES, Inc.285-87 North Sixth St. Brooklyn, N. Y.Tkt PIWEICUROSTAIA husky for handlingreal power. In severalturns of knob, it coverswide range. Handle!up to 40 watts. Inthree ranges to10 ohms. 25-500ohms, 200-100.000ohms. Price S3 50.The STANDARD CLAROSTATThe ideal B-voltage tapcontrol, providing theprecise voltage for eachcircuit and for any typeof tube. Universal resistancerange of frompractically to 5,000.000ohms, with a current carryingcapacity of 20 watts.Noiseless. nonpackinf*.foolproof and indestructiblewithin its workingcapacity, Price S2.25WHAT KIT SHALL I BUY? (Continued)220. BROWNING-DRAKE Five tubes; one stage tunedradio frequency (Rice neutralization), regenerative detectorR ELECTROLYTICR25I.2. THERMO-ELEMENT. THERMO-COUPLE A transmitter is described which uses the ArmstrongQST. April, 1927. Pp. 31-32. DKVHIK. tuned-grid tuned-plate circuit. It is said to be capable of a"A Sensitive Thermo-Couple," B. J. Chromy.quick change to either the 20-, the 40-, or the 8o-meter bandA very inexpensive and useful thermo-couple, made of (1500-, 750-, or 3750-kc. band) by means of plug-in coils.tellurium and platinum wire, is described. The method of Tubes giving an output power up to 7.5 watts may be usedconstructing the device and calibrating its range, together with the apparatus. Complete circuit diagrams, methods cfwith a wiring diagram and experimental data, are given. tuning, and operation data are given.RECTIFIERS. RECTIFIERS,375.3.QST. April, 1927. Pp. 34-38. Dry Electrolytic." Developments in Dry Electrolytic Rectifiers," R. S.Kruse.(tickler control), three stages of audio (special combination A new type of rectifier, using a combination of copper,of resistance- and impedance-coupled audio). Two controls magnesium, and composition discs (the last mentionedconsisting of zinc selenide and copper selenide, among other221. LR4 ULTRADYNE Nine-tube super-heterodyne; onethings), has been perfected for A battery chargers up tostage of tuned radio frequency, one modulator, one oscillator,3 amperes output, and also for A battery substitutes, asthree intermediate-frequency stages, detector, and two stated. Complete details concerning mechanical and electricalcharacteristics of this new type of dry rectifier aretransformer-coupled audio stages.222. GREIFF MULTIPLEX Four tubes (equivalent to six given.tubes); one stage of tuned radio frequency, one stage ojtransformer-coupled radio frequency, crystal detector, two Roo7.i. UNITED STATES LAWS AND REGULATIONS. LAWS,stages of transformer-coupled audio, and one stage of QST. April, 1927. Pp. 39-44. Radio Act, 1917.impedance-coupled audio. Two controls. Price complete "The New Radio Law, 'Theparts, $50.00.complete text of the new Radio Law, as enacted by223. PHONOGRAPH AMPLIFIER A five-tube amplifier devicehaving an oscillator, a detector, one stage of trans-Congress in February, 1927, is printed for the benefit of thereaders of QST.former-coupled audio, and two stages of impedance-coupled Rii3-5. METEOROLOGICAL. METEOROLOGY,audio. The phonograph signal is made to modulate the057" April, 1927. Pp. 45-46. Distance Calculations.oscillator in much the same manner as an incoming signal "How Far Is It?" C. C. Knight.from an antenna.A method whereby distances on the earth's surface fromplace to place may be determined with accuracy, is outlinedin terms of spherical trignometric formulas. As stated, theUSE THIS COUPON FOR KITSplan is very simple and the average person may obtain verygood results using these formulas. Distance on flat maps arevery inaccurate ordinarily, since it is difficult to makeRADIO BROADCAST SERVICE DEPARTMENTallowances for the curvature of the earth.Garden City, New York.Please send me information about theR26i. ELECTRON-TUBE VOLTMETERS. VOLTMETER,following kits indicatedby number:QST. April, 1927, Pp. 47-53- Electron-Tube"The Most Useful Meter," R. F. Shea.A comparison made between ordinary types of metersused in radio measurements and the vacuum-tube voltmetershows how far superior the latter is when making accuratetests for small current and voltage values. Five types ofcommercial vacuum-tube voltmeteis, their apparatus, andcircuit arrangement, and their operation, are outlined indetail. The following are some of the many measurementsthat can be made with this handy instrument : ( i ) Obtaininggain through a radio-frequency or audio-frequency amplifier;(2) Checking the wave form of an oscillator; (3) MeasuringName.high impedance; (4) Employing it as a wavemeter ofhigh precision.Address(Number)(Street)R38i. CONDENSERS. CONDENSERS,QST. April, 1927. Pp. 55-57- Electrolytic." "Electrolytic Filter Condensers, L. F. Lenck.The(City)(State)operation of electrolytic filter condensers, employingaluminumORDER BY NUMBER"pie-plates" and ammonium phosphate in theirONLY. This coupon must Imake-up in smoothing out the lectified a. c., is outlined.accompany each order.The method of forming plates and precautions to take inRBio27getting good results are discussed in detail.R344.4. SHORT-WAVE GENERATORS. TRANSMITTER,RADIO BROADCAST. April, 1927. Pp. 57O-573- Slort-Wavt."A 20 40 80 Meter Transmitter," K. Henney.Supplementing data given in the April, 1926, and Nov.1926, RADIO BROADCAST, on the construction and operationof a short-wave transmitter, additional informationA KEY TO RECENTis presentedconcerning a similar set which operates from thepower mains, using two 216-6 rectifiers and two ux-2looscillators. The circuit is of the well-known Hartley pattern.Considerable information on details of construction is presentedso that any one interested in transmitters may setRADIO ARTICLESup the outfit. Data on DeForest transmitter tubes are alsogiven.By E. G. SHALKHAUSERR35i. SIMPLE OSCILLATORS.OSCILLATOR,THIS is the twenty-third installment of references QST. March, 1927. Pp. 23-27. Calibrator.to articles which have appeared recently in variousradio periodicals. Each separate reference"Quartz Crystal Calibrators, A. Crossley.Two circuits, in which the quartz crystal may be used toshould be cut out and pasted on 4" x 6" cards set up continuous oscillations, are discussed. These employfor either a crystal placed between plate and grid or betweenfiling, or pasted in a scrap book either alphabeticallynumerically. An outline of the preferred, With large inductance and small capacitygrid and filament of a vacuum tube, the latter method beingDeweythe phase adjustingDecimal System (employed here) appeared last inplate, many harmonicsare said to beobtainable. Thecrystal calibrator, as described,the January RADIO BROADCAST.may be used to measure accurately inductances, capacities,frequency meters, transmitters, etc.R536 MINING. MINING AND RADIO.Radio. Feb., 1927. Pp. 28-ff."Experiments in Radio Prospecting, "J. G. Alverson.The author gives some of his findings regarding the propagationof radio waves through the crust of the earth,R344-4. SHORT-WAVE GENERATORS. TRANSMITTER,Q5/. April, 1927. Pp. 15-16. fShort-Wave.showing how the wave-front of the electromagnetic wave"A 15-Meter Commercial Station-2 XS."changes with a change in rock, earth, and minerals. DataThe General Electric station 2 XS, operating on i 5 meters, are presented of many observations made with a smallbuilt for the purpose of transmitting to Buenos Aires 365days in the year, regardless of weather conditions, is described.The set is rated at 7 kw. and radiates its energytransmitter operating on a wavelength of looo meters (300kc.) and using an ordinary type receiver.from a horizontal doublet with reflector.R343 5. SUPER-HETERODYNE SETS. SUPER-HETERODYNE,Radio. Feb., 1927. Pp. 25-ff. Best 1927 Model.Ri34. DETECTOR ACTION DETECTOR ACTION."The 1927 Model of Best's Super-Heterodyne," G. M.QST, April, 1927. Pp. 17-18.Best."Which Is the Detector Tube?" L. W. Hatry.The improved model of Best's super-heterodyne receiverThe difference in operation of detectors and amplifiers in is outlined foi the set builder. The set consists of nine tubes,standard radio circuits is discussed. Whether a tube functionsas a detector as an amplifier, or both, depends uponwith two tuning dials, and is completelyvarious factors in the circuit, such as grid return, connectionof grid leak, etc.Ro84. MAPS AND CHARTS.CHART,Radio. Feb., 1927. Pp. 140-141. L, C, f Data.R330. ELECTRON TUBES. ELECTRON TUBES. "Chart for Radio Circuit Calculations," E. L. Hall.AQST. April, 1927. Pp. 26-30. UX-240.graphic chart, showing the relation between frequency,"CX-340 UX-240," R- S. Kruse.inductance, and capacitance for values as used in radioIn making a comparison between the ux-2oi-A and the ciicuits, is diawn for purposes of rapid calculation. Thenew ux-24O amplifier tube, the writer presents the details accuracy of results obtainable may be within several perupon which good amplification depends, namely: (i) The cent, of the mathematical calculation, as stated. The rangeamplification constant of the tube; (2) the plate impedance may be extended beyond those actually shown by a simpleof the tube; (3) the impedance of the transformer. The process.ux-240 is said to be excellent for c. w. and for resistancecoupledbroadcast sets. As a detector, this new tube is said R350. GENERATING APPARATUS;to eliminate considerable interference because of its peak TRANSMITTING SETS.characteristics.QST. March, 1927. Pp. 33-3?- TRANSMITTER,"A Flexible Transmitter," F. J. Marco. Hexible.

RADIO BROADCAST ADVERTISER 399Most popularB FWer Unit/orradio sets inthe^orld7he Super B, illustrated aboveis only $29$?, complete with^Cajesiic Super-Power-Rectifierliibe.GRIJNOV^ HINDS " CO,4572 ARMITAGE AVE, CHICAGO-ILL

400 RADIO BROADCAST ADVERTISERRi 13.5. METEOROLOGICAL. METEOROLOGY.Proc. I. R. E. Feb., 1927, Pp. 83-97."The Correlation of Radio Reception with Solar Activityand Terrestrial Magnetism," G. W. Pickard.Atmospheric changes and the resulting magnetic stormsaffecting radio reception are discussed. Atmospheric changesare said to be due to radiations and emissions from the sun.The author compares observed radio reception data, obtainedover a continuous period, with meteorological data,and finds a close correlation of sunspot disturbances andradio reception on the upper broadcast wave spectra.Graphs drawn from observed data obtained from stationWBB.M show that, when average results are compared withmagnetic storms, both variations appear to be more or lessin phase.Rim. GENERAL METHODS AND APPARATUS. MEASUREMENTS,Proc. /. R. E. Feb.,11927. Pp. 90-11. Receiver." Importance of Laboratory Measurements in the Designof Radio Receivers," W. A. MacDonald.A series of thirteen fundamental tests are outlined for determiningindividual and overall characteristics of commercialreceivers. A series of graphs gives the results obtainedfrom a typical circuit and depicts to what degreea high precision standard may be used.Ri34. DETECTOR ACTION.DETECTOR,Proc. I. R. E. Feb., 1927. Pp. 113-153. Action.The NEW Moorish design Pacent Cabinet "A Theoretical andCone Experimental Investigation of Detectionfor Small Signals," E. L. Chaffee and G. H.in two-tone antique finish $o nnmahogany ............ *jiJ' uvBrowning.Data are given on the detecting properties of diode andtriode valves as used in radio circuits. The mathematicalpresentation is expressed in terms of the circuit impedancesand the first and second partial differential coefficientsof the static characteristic curves of the device, taken atthe points on the curves determined by the steady polarizingvoltages. It is then assumed that the impressed signal is sosmall that for any given steady voltages these coefficientscan be assumed constant within the range of the variationdue to the signal voltage.R430. INTERFERENCE ELIMINATION. INTERFERENCE,QST. March, 1927. Pp. 9-14. Elimination."Cures for 'Power Leaks,'" R. S. Kruse.The article states that power leaks and other sources ofhigh-frequency interference may be eliminated by properfiltering. The '"Tobe," the "Dayfan," and other interferenceeliminating devices are described.Ri42.3- INDUCTIVE COUPLED CIRCUITS. TRANSFORMERS.QST. March, 1927. Pp. 20-22.Tuned R.F,"The Theory of a Tuned R. F. Transformer," G. H.Browning and F. H. Drake.A mathematical presentation, supplemented by experimentalcurves of tuned radio-frequency transformers, is given.The results show that the secondary inductance should bemade as large as possible, the losses made very small, andthe primary-secondary capacity kept as low as possible,in order to obtain maximum efficiency.Ri40. RADIO CIRCUITS.MASTER-OSC.QST, March, 1927. Pp. 38-fT. AND POWER-AMP."How Our Tube Circuits Work. Part 4," CIRCUITS.R. S. Kruse.In this fourth of a series of articles on radio circuits thewriter takes up the many phases of oscillator circuits withand without amplifier hook-ups. A variety of subjects dealingwith this type of circuit are taken up, as for instance:"Wobbulatipn," its causes and remedy; steadiness of wavewith and without the use of a crystal; the characteristicsof the Armstrong circuit; single- and multi-stage amplifiersand their use as wave-changers in order to prevent troublesomefeedbacks.R9oo. MISCELLANEOUS.FUTUREPopular Radio. March, 1927. Pp. 229-ff. OF RADIO."Radio in 1950 A. D.," Dr. Lee DeForest.The author enumerates some of the future possibilitiesfound in the stored-up energy of waves as utilized for radiotransmission and reception. The newly discovered cosmicray, having a wavelength of 0.0004 angstrom units, andThe new 17-inch Pacent Balanced Cone establishesa new standard in conestated by Millikan, is said to have many possibilities.traveling at a much greater speed than light waves, asspeaker performance11342.7. AUDIO-FREQUENCY AMPLIFIERS. AMPLIFIERS,Popular Radio. March, 1927. Pp. 253-ff. Audio-" Audio Amplifiers," E. L. Bowles. Frequency.The underlying principles covering audio-frequencyreproduction and amplification are outlined in an elementarydiscussion. Causes and effects of distortion, at either thetransmitting or receiving end, may be corrected, it is said,by proper design and construction of the apparatus.R2oi.s. SHIELDING AND GROUNDING.SHIELDING.Radio News. Feb., 1927. Pp. 988-fF."Shielding in Radio Receivers," M. L. Hartmann andJ. R. Meagher.A brief and elementary discussion on the theory of shieldingof radio receivers is given. Some of the benefits of shieldingare said to be increased amplification, increased selectivity,better neutralization, and decreased body-capacityeffects.R37S- 17S- 3 ELECTROLYTIC RECTIFIERS. K.ECTIFIERS. RECTIFIERS,KECTIFIER:The Transmitter. Dec. il.1927., Pp. lo-ff. Cbemica"Practical Chemical Rectifiers," C. R. Stedman.In constructing a practical chemical rectifier, the writersuggests that pure aluminum should be used. Both the leadThe Pacent PHONOVOX (electric pickup) attachedto your phonograph ami plates, however, should be of the same size.and aluminum radio, reproducesrecords with the tone quality 4 ~* solution recommended is either bicarbonate of sodaThe-j -Qor ammoniumrivaling the electric phonograph ... iL'phosphate. Constructional details and wiringdiagrams are given.Ask your dealer for a demonstrationR342.7. AUDIO-FREQUENCY AMPLIFIERS. AMPLIFIERS,or write us if dealer doesn't handle.Radio " World. Feb., 19, 1927. Pp. 5. Audio-Frequency.More Volume from Lower Ratio in Audio Transformers,a Frequent Condition," K. B. Humphrey.In analyzing the importance of proper relation of audioRADIO CORPORATION156 W. 16th Street, New York CityTONE QUALITY^is their outstandingfeaturethree new Pacentproducts bring a new andkeener enjoyment of radio bythe true fidelity and realismof their reproduction.transformer winding ratios to tube resistance, it is statedthat consideration should be given the various factors involvedfrom an engineering standpoint when selection ismade. Usually, it is said, more volume and less distortionis obtained from properly constructed low-ratio transformersthan those of high ratio.R$$2. TRANSMISSION OF PHOTOGRAPHS. PHOTOGRAPHRadio World. Feb., 26, 1927. Pp. 4-5. TRANSMISSION."First Television Hookups Elucidate Alexanderson andBaird Plans," H. Wall.The Alexanderson and the Baird systems of televisionare shown in schematic diagram. The two systems are comparedand the advantages and disadvantages outlined.Rii3.4. IONIZATION; HEAVISIDE LAYER. HEAVISIDERadio World. Feb., 26, 1927. Pp. 8. LAYER."Radio Ceiling Again Verified."Experiments conducted by the Carnegie Institute regardingthe existence and probable nature of the Kenelly-Heaviside layer have established that such a layer actually existsat an altitude varying between 50 and 130 miles. Whetherthe radio waves are 'reflected or refiacted from this upperlayer is not definitely known. Fading may be explainedon the assumption that interfering waves neutralize eachother.Ro2o. TEXTBOOKS.TEXTBOOKS.The New York Sun. Radio Section. Nov. 6, 1926. Radio."An Expert's 3-Foot Shelf of Radio Books, "S. R. Winter,The following is a list of textbooks and published materialselected by Doctor Dellmger, of the Bureau of Standards,for the radio man:1. "Signalling Through Space Without Wires," H.Hertz.2. "The Principles of Electric Wave Telegraphy and Telephony,"J. A. Fleming."Electric Waves," H. Hertz.3.4. "The Principles Underlying Radio Communication,"Bureau of Standards.5. "Radio Instruments and Measurements," Circular74, Bureau of Standards.6. "Robinson's Manual of Radio Telegraphy," UnitedStates Navy." How to Become a Wireless Operator," Chas. B.7.Hayward.8. " Direction and Position Finding," R. Keen, ofSheffield, EnglancL9. "I. C. S. Handbook for Radio Operators," InternationalCorrespondence Schools.to. "Radio Telephony for Amateurs," S. Ballantine.n. "Radio for Everybody," A. C. Lescarboura.12. "Radio for All," H. Gernsback.13. "Elements of the Mathematical Theory of Electricityand Magnetism," J. J. Thompson.14. "Handbook of Technical Instruction for WirelessTelegraphists," C. Hawkhead and H. M. Dowsett.15. "Wireless Telegraphy and Telephony," H. M. Dowsett.16. "The Thermionic Vacuum Tube and Its Application,"H. J. Von der Bijl.17. "The Radio Amateur's Handbook," F. E. Handy.18. "Yearbook of Wireless Telegraphy," Wireless Press,Ltd. (Published annually).19. "Electromagnetic Oscillations in Oscillators and RadioTelegraphy,"- j. Zenneck.20. "Wireless Telegraphy and Telephony " Chas. R.Gibson.21. "Radio Laws and Regulations of the United States,"U.S. Department of Commerce.22. "The Realities of Modern Science," John Mills.23. "Electric Oscillations and Electric Waves," G. W.Pierce.24. "Principles of Radio Communication," J. H. Morecroft.25. "Principles of Radio Transmission and Reception withAntenna and Coil Aerials," Bureau of Standards.26. "Methods of Measurement of Properties of ElectricalInsulating Materials," Bureau of Standards.27. "Handbook of Safety Rules for Radio Installations,"Bureau of Standards.28. "Wireless Telegraphy and Telephony," W. H. Eccles.29. "Thermionic Tubes in Radio Telegraphy," JohnScott-Taggart.30. "Radio Broadcast's Knockout Receiver," Doubleday,Page and Company.31. "How to Build Your Radio Receiver," Popular RadioPublishing Company.32. "The Radio Service Bulletin," United States Departmentof Commerce. (Monthly).33. Introduction to Line Radio Communication," SignalCorps Pamphlet.34. "Modern Radio Operation," J. O. Smith.35. "TheC. W. Manual," J. B. Dow.36. "Radio for Amateurs," A. H. Verrill.37. "Circular No. 24," Bureau of Standards.38. "Copper Wire Tables,"- Bureau of Standards.39. "The Radio Direction Finder and Its Application toNavigation," Bureau of Standards.40. "Formulas and Tables for the Calculation of Mutualand Self-Inductance," Bureau of Standards.41. "The Outline of Radio," J. V. L. Hogan.42. "Qualitative Experiments in Radio Transmission,"Bureau of Standards.Ri34.8. REFLEX ACTION. REFLEXQST. Feb., 1927. Pp. 21-27. ACTION." Developments in Tuned Inverse Duplex," DavidGrimes. Part 2.In this second of two articles, the Inverse Duplex Systemof amplification in the radio and audio circuits, developedfor duplexing, are discussed. For the audio stage, a transformer-resistance-transformerarrangement is said to bethe most desirable and effective. In order to obtain equalamplification over the entire broadcast band, a radio frequency-audiofrequency filter circuit, comprising a chokecoil and a large fixed condenser, is connected betweenstages. Circuit diagrams and panel layouts are shown.R344-5. ALTERNATING CURRENT SUPPLY. A.C. FORRADIO BROADCAST. Feb., 1927. Pp. 393-396- FILAMENTS."A.C. As a Filament-Supply Source," B. F. Miessner.The writer discusses the problems encountered in lightingthe filaments of radio vacuum tubes from the regulardirect or alternating current obtained from the light socket.Filter systems,devised to eliminate the hum in the a.c.line, which presents many varying characteristics, as shownin graphs, are given. The 1 1 2 type tube, as compared to the199, the 201-A type, and the wx- 12 type, is considered thebest tube to use for radio-ami audio- frequency amplificationin a.c. lighted filament circuits.

RADIO BROADCAST ADVERTISER 40187%At 30 Cycles!CURVE SHOWS TRANSFORMATION OFSILVEP-MAR3HHLL TffANSFORMEKSWHEN OPERATING OUTA TUBE HAVINGA PLATE RESISTANCE OF10.3OO OHMS.plifier for the LC-20 receiver241 with an S-M power supply! uses t!*o 24o's and aIn this standardized Hack shielding case areIIPhoused the famous 220 audio and 121 outputtransformers, 222 output, 230 push-pull input,At jo cycles, an S-M 220 audio transformer in a standard amplifier231 push-pull output, 325 filament. 329, j2pA circuit gives 87% of the amplification obtained at 1000 cycles, while itsand 330 power transformers, 331 Unichoke and curve332 condenser bank. And a new substantially flat from 100 to 1000 cycles. Above 2000 cycles, thesuper-power curve for afull wave ABC supply transformer is on the waysingle stage falls off gradually, while in a standard two stagetype 328, at $18.00, for one or two 2168 or amplifier circuit, the curve is substantially flat up to 5000 cycles above281 tubes.which frequencyit falls off rapidly to keep static, heterodyne squealsand "set noise" at a minimum.The above paragraph sums up at once the desirable characteristics of an audio amplifierfor realistic recreation of broadcast programs, and the actual performance of S-M audiotransformers. It is just this fact that has made 22o's the choice of over half of the designersof the new 1927-1928 circuits, for engineers know that the short cut to the finestof quality is to use S-M audios. Experienced fans know this too, as is proven by the factthat 22o's have outsold every other transformer in their class by a wide margin for over ayear. And S-M audios are signally favored by being used in more broadcasting stationsany other types. WCAE, WBBM, WEBH, KFCR, WTAQ, KGDJ, WLBF, andmany others. WCFL, the "Voice of Labor" checks quality of all programs with them.Sillier- Marshall now offers two smaller size audioNathaniel Baldwin, Inc., famous speaker experts, test with 22o's and 22i's.Your guarantee of quality is to use S-M 220' s and 22i's in every circuit you build, andtransformers for replacement worl^ in old sets,wherever price and size is a consideration. you'll find that over half the popular 1927 and 1928 circuits will give you just this sameType 240audio transformer is equal or guaranteesuperior to the majorityquality. But S-M promises unconditionally that you can improve any set byusing 22o's and 22i's, and back? the promise by the offer of your money back if 22o's andof high-grade audio transformers, but does not22i's don't give you more satisfactory quality than you've ever heard before.reproduce frequencies below So cycles to the extent The 220 audio is the biggest value on the market, and its performance- measures up tothat the famous 220 does. Its single stage amplifier its 4 pound size. It contains more steel and copper than any other transformer the measureof transformer merit. Price $8.00.curve is shown above in two stages, the 243*5 affordpractically the same 5000 cycle cut-ojf as do221 output transformer not only protects loud speakers against power tube plate currents,22o's, althought this is not evident in the singlebut compensates low frequencies for all loud speakers. Price $7.50, or with cordstage curve above. 241 output transformer offers and tip jacks, No. 222, $8.00.the same low frequency compensation as type 221230and 222. Due to their small size, these push-pull input and 231 push-pull output transformers are priced at $10.00 each.transformerswill fit in almost any of the older receivers, and onceinstalled, will wori^ wonders in tone qualitv improvement,The New Shielded Six Is Ready!for their performance nearly equals that Theof fVImproved 22d's and Shielded Six is22i's. Size 3 ready, the very latest model of this excellent receiverhigh, 2\" wide, which has over a year of successful and satisfying performance to its credit. The Improved2j" deep, weight 2 Ibs. 4 ozs. each. Price, 240 audio model has vastly increased selectivity, greater distance getting ability, and the same fine$6.00, 241 output $5.00.tone that has made almost everybuilder say of the original, "That's the finest set I'veLaurence Coc^aday, for the preferred audio am-ever heard!"This year the Six offers the additional possibilities of push-pull amplification with 210tubes for the man who wants the utmost. All in all, the Six deserves the reputation asthe finest tuned R. F. kit you can buy, equalled only by $200 to $400 factory built sets.Yet it's priced at but $95.00 for the complete kit, or $142.00 assembled, in cabinet, andguaranteed to satisfy you. S-M will be glad to tell owners how last year's model can beconverted to the Improved Six, or push-pull 210 amplification installed with simple changes.We can't tell you the whole storydevelopments, so if you'll just fill in the coupon, andmail it with ice to cover postage, we'll send youfree more up-to-the-minute advance radio informationthan you could buy in a text book.of new S-M ---_...SILVER-MARSHALL, Inc.838 West Jackson Blvd., Chicago, U. S. A.Please send me information on new S-Mdevelopments, for which I enclose IDC.Silver-Marshall Inc.,838 West Jackson Blvd. Chicago, U. S. A.NameAddress. .

402 RADIO BROADCAST ADVERTISER"RADIO BROADCASTS" DIRECTORY OFMANUFACTURED RECEIVERSd A coupon will be found on page 416. All readers who desire additionalinformation on the receivers listed below need only insert the proper numbersin the coupon, mail it to the Service Department of RADIO BROADCAST,and full details will be sent. New sets are listed in this space each month.KEY TO TUBE ABBREVIATIONSNO. 484. BOSWORTH, B5stage. Price $125 including power unit. $245.99 60-mA. filament (dry cell)Five tubes; 2 t.r.f. (26), detector (99), 2 transformer01-A Storage battery 0.25 amps, filamentaudio (special a.c. tubes). T.r.f. circuit. Two dials.12 Power tube (Storage battery)Volume control: potentiometer. Cabinet size: 23 x 771 Power tube (Storage battery)x 8 inches. Output device included. Price $175.16-B Half-wave rectifier tube80 Full-wave, high current rectifierNO. 406. CLEARTONE 11081 Half-wave, high current rectifierFive tubes; 2 t.r.f., detector, 2 transformer audio.Hmu High-Mu tube for resistance-coupled audioAll tubes a. c. heater type. One or two dials. Volume20 Power tube (dry cell)control: resistance in r. f. plate. Watts consumed: 40.10 Power Tube (Storage battery)Cabinet size- varies. The plate supply is built in the00-A Special detectorreceiver and requires one rectifier tube. Filament supplythrough step down transformers. Prices range from13 Full-wave rectifier tube26 Low-voltage high-current a. c. tube$175 to $375 which includes 5 a.c. tubes and one rectifier27 Heater type a. c. tubetube.NO. 407. COLONIAL 25DIRECT CURRENT RECEIVERSSix tubes; 2 t. r. f. (01-A), detector (99), 2 resistanceaudio (99). 1 transformer audio (10). Balanced t.r.f.NO. 424. COLONIAL 26circuit. One or three dials. Volume control: AntennaSix tubes; 2 t. r. f. (01-A), detector (12), 2 transformeraudio (01-A and 71). Balanced t. r. f. One to sumed: 100. Console size: 34 x 38 x 18 inches. Outputswitch and potentiometer on 1st audio. Watts con-three dials. Volume control: antenna switch and potentiometeracross first audio. Watts required: 120. Con-the detector which is supplied with rectified a.c. fromdevice. All tube filaments are operated on a. c. exceptsole size: 34 x 38 x 18 inches. Headphone connections. the plate supply. The rectifier employs two 16-B tubes.The filaments are connected in a series parallel arrangement.Price $250 including built-in plate and filament supply.Price $250 including power unit.NO. 507. CROSLEY 602 BANDBOXNO. 425. SUPERPOWERSix tubes; 3 t.r.f. (26), detector (27), 2 transformerFive tubes: All 01-A tubes. Multiplex circuit. Two audio (26 and 71). Neutrodyne circuit. One dial,dials. Volume control: resistance in r. f. plate. Watts Cabinet size: 17} x 5} x 7|- inches. The heaters for therequired: 30. Antenna: loop or outside. Cabinet sizes: a.c. tubes and the 71 filament are supplied by windings intable, 27 x 10 x 9 inches; console, 28 x 50 x 21. Prices: B unit transformers available to operate either on 25 ortable, $135 including power unit; console, $390 includingpower unit and loud rectifier speaker.60 cycles. The plate current is supplied by means oftube. Price $65 for set alone, power unit $60.NO. 408. DAY-FAN "DE LUXE"A. C. OPERATED RECEIVERSSix tubes; 3 t.r.f., detector, 2 transformer audio. AllNO. 508. ALL-AMERICAN 77, 88, AND 99 01-A tubes. One dial. Volume control: potentiometeracross r.f. tubes. Watts consumed: 300. Console size:Six tubes; 3 t. r. f. (26), detector (27), 2 transformer 30 x 40 x 20 inches. The filaments are connected inaudio (26 and 71). Rice neutralized t. r. f.Single drum series and supplied with d.c. from a motor-generatortuning. Volume control: potentiometer in r. f. plate. set which also supplies B and C current. Output device.Price $350 including power unit.Cabinet sizes: No. 77, 21 x 10 x 8 inches; No. 88 Hiboy,25 x 38 x 18 inches; No. 99 console, 27} x 43 x 20 inches.Shielded. Output device. The filaments are suppliedNO. 409. DAYCRAFT 5by means of three small transformers. The plate supplyemploys a gas-filled rectifier tube. Voltmeter in a. c. Five tubes; 2 t.r.f., detector, 2 transformer audio.supply line. Prices: No. 77, $150, including power unit; All a. c. heater tubes. Reflexed t.r.f. One dial. VolumeNo. 88, $210 including power unit; No. 99, $285 includingpower unit and loud speaker.Watts consumed: 135. Console size: 34 x 36 x 14 inches.control: potentiometers in r.f. plate and 1st audio.Output device. The heaters are supplied by means ofNO. 509. ALL-AMERICAN "DUET"; "SEXTET" a small transformer. A built-in rectifier supplies BSix tubes; 2 t. r. f. (99), detector (99), 3 transformer and C voltages. Price $170, less tubes. The followingaudio (99 and 12). Rice neutralized t.r.f. Two dials. have one more r.f. stage and are not reflexed: Daycraft6, $195; Dayrole 6, $235; Dayfan 6, $110. AllVolume control: resistance in r.f. plate. Cabinet sizes:"Duet," 23x 56x16} inches; "Sextet," 22}x 13} x 15} prices less tubes.inches. Shielded. Output device. The 99 filaments areconnected in series and supplied with rectified a.c.,NO. 469. FREED-EISEMANN NR11while 12 is supplied with raw a.c. The plate and filamentsupply uses gaseous rectifier tubes. Millammeter former audio (01-A and 71). Neutrodyne. One dial.Six tubes; 3 t.r.f. (01-A), detector (01-A), 2 trans-on power unit. Prices: "Duet," $160 including power Volume control: potentiometer. Watts consumed: 150.unit; "Sextet," $220 including power unit and loud Cabinet size: 19J x 10 x 10} inches. Shielded. Outputspeaker.device. A special power unit is included employing arectifier tube. Price $225 including NR-411NO. 511. ALL-AMERICAN 80, 90, AND power unit.115Five tubes; 2 t.r.f. (99), detector (99), 2 transformerNO. 487. FRESHMAN 7F-ACaudio (99 and 12). Rice neutralized t.r.f. Two dials. Six tubes; 3 t.r.f. (26), detector (27), 2 transformerVolume control: resistance in r.f. plate. Cabinet sizes: audio (26 and 71). Equaphase circuit. One dial. VolumeNo. 80, 231 x 12} x 15 inches; No. 90, 371 x 12 x 121 control: potentiometer across 1st audio. Console size:inches; No. 115 Hiboy, 24 x 41 x 15 inches. Coils individuallyshielded. Output device. See No. 509 for24} x 41} x 15 inches. Output device. The filaments andheaters and B supply are all supplied by one power unit.power supply. Prices: No. 80, $135 including power The plate supply requires one 80 rectifier tube. Priceunit; No. 90, $145 including power unit and compartment;No. 115, $170 including power unit, compart-$175 to $350, complete.ment, and loud speaker.NO. 536. SOUTH BENDNO. 510. ALL-AMERICAN 7Six tubes. One control. Sub-panel shielding. BindingPosts. Antenna: outdoor. Prices: table, $130, BabySeven tubes; 3 t.r.f. (26), 1 untuned r.f. (26), detector Grand console, $195.(27), 2 transformer audio (26 and 71). Rice neutralizedt.r.f. One drum. Volume control: resistance in r.f.NO. 537. WALBERT 26plate. Cabinet sizes: "Sovereign" console, 30} x 60}x 19 inches; "Lorraine" Hiboy, 251 x 53j x Six17} inches;tubes; five Kellogg a.c. tubes and one 71. Two"Forte" cabinet, 25} x 13} x 17} inches. For filament controls. Volume control: variable plate resistance.and plate supply: See No. 508. Prices: Isofarad circuit. "Sovereign"Output device. Battery cable. Semishielded.Antenna: 50 to 75 feet. Cabinet size: 10 J x$460; "Lorraine" $360; "Forte" $270. All prices includepower unit. First two include loud speaker.29} x 16} inches. Prices: $215; with tubes, $250.NO. 403. ARGUS 250BNO. 538. NEUTROWOUND, MASTER ALLECTRICSix tubes; 2 t.r.f. (99), 1 untuned r.f. (99), detector Six tubes; 2 t.r.f. (01-A), detector (01-A), 2 audio(99), 2 transformer audio (99 and 12). Stabilized with (01-A and two 71 in push-pull amplifier). The 01-Agrid resistances. Two dials. Volume control: resistance tubes are in series, and are supplied from a 400-mA.across 1st audio. Watts required: 100. Cabinet size: rectifier. Two drum controls. Volume control: variable35J x 14| x 10J inches. Output device. The 99 filaments plate resistance. Output device. Shielded. Antenna:are connected in series and supplied with rectified a.c.,while the 12 is run on raw a.c. The power unit requirestwo 16-B rectifier tubes. Milliammeter included in d.c.50 to 100 feet. Price: $360.NO. 545. NEUTROWOUND, SUPER ALLECTRICsupply. Price $250.00 including self-contained power unit.FiveOther models: No. tubes; 2 t.r.f.125, $125.00; console (99), detector (99), 2 audio (99model, $375.00. and 71). The 99 tubes are in series and are supplied fromNO. 401. AMRAD AC9an 85-mA. rectifier. Two drum controls. Volume control:variable plate resistance. Output device. Antenna:Six tubes; 3 t.r.f. (99), detector (99), 2 transformer 75 to 100 feet. Cabinet size: 9 x 24 x 11 inches. Price:(99 and 12). Neutrodyne. Two dials. Volume control:$150.resistance across 1st audio. Watts consumed: 50. Cabinetsize: 27 x 9 x 11 J inches. The 99 filaments are connectedNO. 490. MOHAWKin series and supplied with rectified a.c., while Six tubes; 2 t.r.f., detector, 2 transformer audio. Allthe 12 is run on raw a.c. The power unit, requiring two tubes a.c heater type except 71 in last stage. One dial.16-B rectifiers, is separate and supplies A, B, and C Volume control: rheostat on r.f. Watts consumed: 40.current. Price $142 including power unit.Panel size: 12} x 8f inches. Output device. The heatersfor the a.c tubes and the 71 filament are suppliedNO. 402. AMRAD ACSbysmall transformers. The plate supply is of the built-inFive tubes. Same as No. 401 except one less r.f. type using a rectifier tube. Prices range from $65 toNO. 413.MARTISix tubes: 2 t.r.f., detector, 3 resistance audio. Alltubes a.c. heater type. Two dials. Volume control:resistance in r.f. plate. Watts consumed : 38. Panel size7 x 21 inches. The built-in plate supply employs one16-B rectifier. The filaments are supplied by a smalltransformer. Prices: table, $235 including tubes andrectifier; console, $275 including tubes and rectifier;console, $325 including tubes, rectifier, and loud speaker.NO. 417 RADIOLA 28Eight tubes; five type 99 and one type 20. Drumcontrol. Super-heterodyne circuit. C-battery connections.Battery cable. Headphone connection. Antenna:loop. Set may be operated from batteries or from thepower mains when used in conjunction with the model104 loud speaker. Prices: $260 with tubes, batteryoperation; $570 with model 104 loud speaker, a. c.operation.NO. 540 RADIOLA 30-AReceiver characteristics same as No. 417 except thattype 71 power tube is used. This model is designed tooperate on either a. c. or d. c. from the power mains.The combination rectifier power amplifier unit usestwo type 81 tubes. Model 100-A loud speaker is containedin lower part of cabinet. Either a short indooror long outside antenna may be used. Cabinet size:42'/2 x 29 x 17% inches. Price: $495.NO. 541 RADIOLA 32This model combines receiver No. 417 with the model104 loud speaker. The power unit uses two type 81tubes and a type 10 power amplifier. Loop is completelyenclosed and is revolved by means of a dial on the panel.Models for operation from a. c. or d. c. power mains.Cabinet size: 52 x 72 x 17% inches. Price: $895.NO. 539 RADIOLA 17Six tubes; 3 t. r. f. (26), detector (27), 2 transformeraudio (26 and 27). One control. Illuminated dial.Built-in power supply using type 80 rectifier. Antenna:100 feet. Cabinet size: 25A x 7% x 8'/8 . Price: $130without accessories.NO. 421. SOVEREIGN 238Seven tubes of the a.c. heater type. Balanced t.r.f.Two dials. Volume control: resistance across 2nd audio.Watts consumed: 45. Console size: 37 x 52 x 15 inches.The heaters are supplied by a small a. c. transformer,while the plate is supplied by means of rectified a.cusing a gaseous type rectifier. Price $325, includingpower unit and tubes.NO. 517. KELLOGG 510, 511, AND 512Seven tubes; 4 t.r.f., detector, 2 transformer audio.All Kellogg a.c. tubes. One control and special zoneswitch. Balanced. Volume control: special. Output device.Shielded. Cable connection between power supplyunit and receiver. Antenna: 25 to 100 feet. Panel 7|jjx 27} inches. Prices: Model 510 and 512, consoles. $495complete. Model 511, consolette, $365 without loudspeaker.NO. 496.SLEEPER ELECTRICFive tubes; four 99 tubes and one 71. Two controls.Volume control: rheostat on r.f. Neutralized. Cable.Output device. Power supply uses two 16-B tubes.Antenna: 100 feet. Prices: Type 64, table, $160; Type65, table, with built-in loud speaker, $175; Type 66,table, $175; Type 67, console, $235; Type 78, console,$265.NO. 522. CASE, 62 B AND 62 CMcCullough a.c. tubes. Drum control. Volume control;variable high resistance in audio system. C-batteryconnections. Semi-shielded. Cable. Antenna: 100 feet.Panel size: 7 x 21 inches. Trices: Model 62 B, completewith a.c. equipment, $185; Model 62 C, complete witha.c. equipment, $235.NO. 523.CASE, 92 A AND 92 CMcCullough a.c. tubes. Drum control. Inductivevolume control. Technidyne circuit. Shielded. Cable.C-battery connections. Model 92 C contains outputdevice. Loop operated. Prices: Model 92 A, table, $350;Model 92 C, console, $475.BATTERY OPERATED RECEIVERSNO. 512. ALL-AMERICAN 44, 45, AND 66Six tubes; 3 t.r.f. (01-A, detector) 01-A, 2 transformeraudio (01-A and 71). Rice neutralized t.r.f. Drumcontrol. Volume control: rheostat in r.f. Cabinet sizes:No. 44, 21 x 10 x 8 inches; No. 55, 25 x 38 x 18 inches;No. 66, 27} x 43 x 20 inches. C-battery connections.Battery cable. Antenna: 75 to 125 feet. Prices: No. 44,$70; No. 55, $125 including loud speaker; No. 66, $200including loud speaker.NO. 428.AMERICAN C6Five tubes; 2 t.r.f, detector, 2 transformer audio.All 01-A tubes. Semi balanced t.r.f. Three dials. Platecurrent 15 mA. Volume control: potentiometer. Cabinetsizes: table, 20 x 8} x 10 inches; console, 36 x 40 x 17inches. Partially shielded. Battery cable. C-batteryconnections. Antenna: 125 feet. Prices: table, $30;console, $65 including loud speaker.

RADIO BROADCAST ADVERTISER 403Above iswiththe master Ray-O-Vac 45-volt "B" battery,the new construction, made especially forsetsusing fouror more tubes.Improve Receptionand reduce operating expenseEMINENT engineers say that forthe best radio reception the "B"power supply should have as little internalresistance as possible.Otherwise signals are liable to be distortedin amplification, and natural,rounded tones cannot come out of theloud speaker.The specialformula used in makingRay-O-Vacs produces batteries thathave only from % to Vs the internalresistance of ordinary sources of "B"power supply.At the same time, this special formulamakes batteries that deliver a strong,steady voltage over an unusually longtime. It gives them staying power.And the long-life of Ray-O-Vac batteriesis now still longer, because anew method of construction preventsinternal short circuits and prolongsthe life of the battery from 10% to15%.There are twice as many radio ownersusing Ray-O-Vacs today as therewere a year ago. They know whatlow internal resistance and stayingpower in "B" batteries mean.Ray-O-Vac batteries are sold by theleading dealers in radio equipmentand supplies.If you have any difficultygetting them write us for thename of a nearby dealer who can supplyyou.FRENCH BATTERY COMPANYMADISON, WISCONSINmakers offlashlights and batteriesand ignition batteries

otor404 RADIO BROADCAST ADVERTISERBOSWORTH B6NO. 485.Five tubes; 2 t.r.f. (01-A), detector (01-A), 2 transformeraudio (01-A and 71). Two dials. Volume control:variable grid resistances. Battery cable. C batteryconnections. Antenna: 25 feet or longer. Cabinet size15 x 7 x 8 inches. Price $75.NO. 513.COUNTERPHASE SIXSix tubes; 3 t.r.f. (01-A), detector (00-A), 2 transformeraudio (01-A and 12). Counterphase t.r.f. Twodials. Plate current: 32 mA. Volume control: rheostaton 2nd and 3rd r.f. Coils shielded. Battery cable. C-battery connections. Antenna: 75 to 100 feet. Consolesize: 18} x 40} x 15} inches. Prices: Model 35, table,$110; Model 37, console, $175.NO. 514.COUNTERPHASE EIGHTEight tubes; 4 t.r.f. (01-A), detector (00-A), 2 transformeraudio (01-A and 12). Counterphase t.r.f. Onedial. Plate current: 40 mA. Volume control: rheostat in1st r.f. Copper stage shielding. Battery cable. C-batteryconnections. Antenna: 75 to 100 feet. Cabinet size:30 x 12} x 16 inches. Prices: Model 12, table, $225;Model 16, console, $335; Model 18, console, $365.NO. 506. CROSLEY 601 BANDBOXSix tubes; 3 t.r.f., detector, 2 transformer audio. All01-A tubes. Neutrodyne. One dial. Plate current:40 mA. Volume control: rheostat in r.f. Shielded.Battery cable. C-battery connections. Antenna: 75 to150 feet. Cabinet size: 17J x 5j x 7}. Price, $55.NO. 434. DAY-FAN 6Six tubes; 3 t.r.f. (01-A), detector (01-A), 2 transformeraudio (01-A and 12 or 71). One dial. Platecurrent: 12 to 15 mA. Volume control: rheostat on r.f.Shielded. Battery cable, C battery connections. Outputdevice. Antenna: 50 to 120 feet. Cabinet sizes: Daycraft6, 32 x 30 x 34 inches; Day-Fan Jr., 15 x 7 x 7.Prices: Day-Fan 6, $110; Daycraft 6, $145 includingloud speaker; Day-Fan Jr. not available.NO. 435. DAY-FAN 7Seven tubes; 3 t.r.f. (01-A), detector (01-A), 1 resistanceaudio (01-A), 2 transformer audio (01-A and 12or 71). Plate current: 15 mA. Antenna: outside. Sameas No. 434. Price $115.NO. 503.FADA SPECIALSix tubes; 3 t.r.f. (01-A), detector (01-A), 2 transformeraudio (01-A and 71). Neutrodyne. Two drumcontrol. Plate current: 20 to 24mA. Volume control:rheostat on r.f. Coils shielded. Battery cable. C-batteryconnections. Headphone connection. Antenna: outdoor.Cabinet size: 20} x 13f x 101 inches. Price $95.NO. 504. FADA 7Seven tubes; 4 t.r.f. (01-A), detector (01-A), 2 transformeraudio (01-A and 71). Neutrodyne. Two drumcontrol. Plate current: 43mA. Volume control: rheostaton r.f. Completely shielded. Battery cable. C-batteryconnections. Headphone connections. Output device.Antenna: outdoor or loop. Cabinet sizes: table, 25 i x13i x 11* inches; console, 29 x 50 x 17 inches. Prices:table, $185; console, $285.NO. 436.FEDERALFive tubes; 2 t.r.f. (01-A), detector (01-A), 2 transformeraudio (01-A and 12 or 71). Balanced t.r.f. Onedial. Plate current: 20.7 mA. Volume control: rheostaton r.f. Shielded. Battery cable. C-battery connections.Antenna: loop. Made in 6 models. Price varies from$250 to $1000 including loop.NO. 505. FADA 8Eight tubes. Same as No. 504 except for one extrastage of audio and different cabinet. Prices: table, $300;console, $400.NO. 437.FERGUSON 10ASeven tubes; 3 t.r.f. (01-A), detector (01-A), 3 audio(01-A and 12 or 71). One dial. Plate current: 18 to 25mA. Volume control: rheostat on two r.f. Shielded.Battery cable. C-battery connections. Antenna: 100feet. Cabinet size: 21} x 12 x 15 inches. Price $150.NO. 438. FERGUSON 14Ten tubes; 3 untuned r.f., 3 t. r.f. (01-A), detector(01-A), 3 audio (01-A and 12 or 71). Special balancedt.r.f. One dial. Plate current: 30 to 35 mA. Volume control:rheostat in three r.f. Shielded. Battery cable, C-battery connections. Antenna: loop. Cabinet size:24 x 12 x 16 inches. Price $235, including loop.NO. 439. FERGUSON 12Six tubes; 2 t.r.f. (01-A), detector (01-A), 1 transformeraudio (01-A), 2 resistance audio (01-A and 12or 71). Two dials. Plate current: 18 to 25 mA. Volumecontrol: rheostat on two r.f. Partially shielded. Batterycable. C-battery connections. Antenna: 100 feet.Cabinet size: 22} x 10 x 12 inches. Price $85. Consolette$145 including loud speaker.NO. 440. FREED EISEMANN NR-8, NR 9, ANDNR-66Six tubes; 3 t.r.f. (01-A), detector (01-A). 2 transformeraudio (01-A and 71). Neutrodyne. NR-8, twodials; others one dial. Plate current: 30 mA. Volumecontrol: rheostat on r.f. NR-8 and 9: chassis typeshielding. NR-66, individual stage shielding. Batterycable. C-battery connections. Antenna: 100 feet.Cabinet sizes: NR-8 and 9, 19 f x 10 x 10} inches; NR-6620 x 10} x 12 inches. Prices: NR-8, $90; NR-9, $100;NR-66, $125.NO. 501. KING "CHEVALIER"Six tubes. Same as No. 500. Coils completely shielded.Panel size: 11 x 7 inches. Price, $210 including loudspeaker.FREED EISEMANN NR-77NO. 441.Seven tubes; 4 t.r.f. (01-A), detector (01-A), 2transformer audio (01-A and 71). Neutrodyne. Onedial. Plate current: 35 mA. Volume control: rheostat onr.f. Shielding. Battery cable. C-battery connections.Antenna: outside or loop. Cabinet size: 23 x 10} x 13inches. Price $175.NO. 442. FREED-EISEMANN 800 AND 850Eight tubes; 4 t.r.f. (01-A), detector (01-A), 1 transformer(01-A), 1 parallel audio (01-A or 71). Neutrodyne.One dial. Plate current: 35 mA. Volume control:rheostat on r.f. Shielded. Battery cable. C-batteryconnections. Output: two tubes in parallel or one powertube may be used. Antenna: outside or loop. Cabinetsizes: No. 800, 34 x 15} x 13} inches; No. 850, 36 x 65} x17}. Prices not available.NO. 444.GREBE MU-1Five tubes; 2 t.r.f. (01-A), detector (01-A), 2 transformeraudio (01-A and 12 or 71). Balanced t.r.f. One,two, or three dials (operate singly or together). Platecurrent: 30mA. Volume control: rheostat on r.f. Binocularcoils. Binding posts. C-battery connections.Antenna: 125 feet. Cabinet size: 22} x 91 x 13 inches.Prices range from $95 to $320.NO. 426.HOMERSeven tubes; 4 t.r.f. (01-A); detector (01-A or OOA);2 audio (01-A and 12 or 71). One knob tuning control.Volume control : control in antenna circuit. Platecurrent : 22 to 25 mA. "Technidyne" circuit. Completelyenclosed in aluminum box. Battery cable. C-battery connections.Cabinet size, 8 x 19} x 91 inches. Chassis size,6f x 17 x 8 inches. Prices: Chassis only, $80. Table cabinet,$95.NO. 502. KENNEDY ROYAL 7. CONSOLETTESeven tubes; 4 t.r.f. (01-A), detector (00-A), 2 transformeraudio (01-A and 71). One dial. Plate current:42 mA. Volume control: rheostat on two r.f. Specialr.f. coils. Battery cable. C-battery connections. Headphoneconnection. Antenna: outside or loop. Consolettesize: 36} x 35} x 19 inches. Price $220.NO. 498.KING "CRUSADER"Six tubes; 2 t.r.f. (01-A), detector (00-A), 3 transformeraudio (01-A and 71). Balanced t.r.f. One dial.Plate current: 20 mA. Volume control: rheostat on r.f.Coils shielded. Battery cable. C-battery connections.Antenna: outside. Panel: 11 x 7 inches. Price, $115.NO. 499.KING "COMMANDER"Six tubes; 3 t.r.f. (01-A), detector (00-A), 2 transformeraudio (01-A and 71). Balanced t.r.f. One dial.Plate current: 25 mA. Volume control: rheostat on r.f.Completely shielded. Battery cable. C-battery connections.Antenna: loop. Panel size: 12 x 8 inches.Price $220 including loop.NO. 429.KING COLE VII AND VIIISeven tubes; 3 t.r.f., detector, 1 resistance audio, 2transformer audio. All 01-A tubes. Model VIII has onemore stage t.r.f. (eight tubes). Model VII, two dials.Model VIII, one dial. Plate current: 15 to 50 mA.Volume control: primary shunt in r.f. Steel shielding.Battery cable and binding posts. C-battery connections.Output devices on some consoles. Antenna: 10 to 100feet. Cabinet size: varies. Prices: Model VII, $80 to$160; Model VIII, $100 to $300.NO. 500.KING "BARONET" AND "VIKING"Six tubes; 2 t.r.f. (01-A), detector (00-A), 3 transformeraudio (01-A and 71). Balanced t.r.f. One dial.Plate current: 19 mA. Volume control: rheostat in r.f.Battery cable. C-battery connections. Antenna: outside.Panel size: 18 x 7 inches. Prices: "Baronet," $70;"Viking," $140 including loud speaker.NO. 489.MOHAWKSix tubes; 2 t.r.f. (01-A), detector (00-A), 3 audio(01-A and 71). One dial. Plate current: 40 mA. Volumecontrol: rheostat on r.f. Battery cable. C-battery connections.Output device. Antenna: 60 feet. Panel size:12} x 8j inches. Prices range from $65 to $245.NORBERT "MIDGET"NO. 449.One multivalve tube; detector, 2 transformer audio.Two dials. Plate current: 3 mA. Volume control: rheostat.Binding posts. C-battery connections. Headphoneconnection. Antenna: 75 to 150 feet. Cabinet size:12 x 8 x 9 inches. Price $12 including multivalve.NO. 450. NORBERT 2Two tubes; 1 t.r.f., detector, 2 transformer audio.One multi-valve tube and one 01-A. Two dials. Platecurrent: 8 mA. Volume control: special. Battery cable.Headphone connection. C-battery connections. Antenna:50 to 100 feet. Cabinet size: 20 x 7 x 5} inches.Price $40.50 including multivalve and 01-A tube.NO. 452. ORIOLE 90Five tubes; 2 t.r.f., detector, 2 transformer audio.All 01-A tubes. "Trinum" circuit. Two dials. Platecurrent: 18 mA. Volume control: rheostat on r. f.Battery cable. C-battery connections. Antenna: 50 to100 feet. Cabinet size: 25} x 11} x 12} inches. Price$85. Another model has 8 tubes, one dial, and isshielded. Price $185.NO. 453.PARAGONSix tubes; 2 t.r.f. (01-A), detector (01-A), 3 doubleimpedance audio (01-A and 71). One dial. Plate current:40 mA. Volume control: resistance in r.f. plate.Shielded. Battery cable. C-battery connections. Outputdevice. Antenna: 100 feet. Console size: 20 x 46x 17 inches. Price not determined.NO. 543 RADIOLA 20Five tubes; 2 t. r. f. (99), detector (99), two transformeraudio (99 and 20).Regenerative detector. Twodrum controls. C-battery connections. Battery cable.Antenna: 100 feet. Price: $78 without accessories.NO. 480. PFANSTIEHL 30 AND 302Six tubes; 3 t.r.f. (01-A), detector (01- 2A), transformeraudio (01-A ind 71). One dial. Plate current:23 to 32 mA. Volume control: resistance in r.f. plate.Shielded. Battery cable. C-battery connections. Antenna:outside. Panel size: 17J x 8} inches. Prices: No.30 cabinet, $105; No. 302 console, $185 including,loud speaker.NO. 515. BROWNING-DRAKE 7-ASeven tubes; 2 t.r.f. (01-A), detector (00-A), 3 audio(Hmu, two 01-A, and 71). illuminated drum control.Volume control: rheostat on 1st r.f. Shielded. Neutralized.C-battery connections. Battery Cable. Metalpanel. Output device. Antenna: 50-75 feet. Cabinet,30 x 11 x 9 inches. Price, $145.NO. 516. BROWNING-DRAKE 6-ASix tubes; 1 t.r.f. (99), detector (00-A), 3 audio(Hmu, two 01-A and 71). Drum control with auxiliaryadjustment. Volume control: rheostat on r.f. Regenerativedetector. Shielded. Neutralized. C-battery connections.Battery cable. Antenna: 50-100 feet. Cabinet,25 x 11 x9. Price $105.NO. 518.KELLOGG "WAVE MASTER,"504, 505, AND 506.Five tubes; 2 t.r.f., detector, 2 transformer audio.One control and special zone switch. Volume control:rheostat on r.f. C-battery connections. Binding posts.Plate current: 25 to 35 mA. Antenna: 100 feet. Panel:7} x 25} inches. Prices: Model 504, table, $75, lessaccessories. Model 505, table, $125 with loud speaker.Model 506, consolette, $135 with loud speaker.NO. 519. KELLOGG, 507 AND 508.Six tubes, 3 t.r.f., detector, 2 transformer audio. Onecontrol and special zone switch. Volume control: rheostaton r.f. C-battery connections. Balanced. Shielded.Binding posts and battery cable. Antenna: 70 feet.Cabinet size: Model 507, table, 30 x 13J x 14 inches.Model 508, console, 34 x 18 x 54 inches. Prices: Model507, $190 less accessories. Model 508, $320 with loudspeaker.NO. 427. MURDOCK 7Seven tubes; 3 t.r.f. (01-A), detector (01-A), 1 transformerand 2 resistance audio (two 01-A and 12 or 71)-One control. Volume control: rheostat on r.f. Coilsshielded. Neutralized. Battery cable. C-battery connections.Complete metal case. Antenna: 100 feet.Panel size: 9 x 23 inches. Price, not available.NO. 520. BOSCH 57Seven tubes; 4 t.r.f. (01-A), detector (01-A), 2 audio(01-A and 71). One control calibrated in kc. Volumecontrol: rheostat on r.f. Shielded. Battery cable. C-bcttery connections. Balanced. Output device. Built-inloud spea'.ier. Antenna: built-in loop or outside antenna,ICO feet. Cabinet size: 46 x 16 x 30 inches. Price: $3-10including enclosed loop and loud speaker.NO. 521. BOSCH "CRUISER," 66 AND 76Six tubes; 3 t.r.f. (01-A), detector (01-A), 2 audio(01-A and 71). One control. Volume control: rheostaton r.f. Shielded. C-battery connections. Balanced.Battery cable. Antenna: 20 to 100 feet. Prices: Model66, table, $99.50. Model 76, console, $175; with loudspeaker $195.NO. 524. CASE, 61 A AND 61 CT.r.f. Semi-shielded. Battery cable. Drum control.Volume control: variable high resistance in audio system.Plate current: 35 mA. Antenna: 100 feet. Prices:Model 61 A, $85; Model 61 C, console, $135.NO. 525. CASE, 90 A AND 90 CDrum control. Inductive volume control. Technidynecircuit. C-battery connections. Battery cable. Loopoperated. Model 90-C equipped with output device.Prices: Model 90 A, table, $225; Model 90 C, console,$350.NO. 526. ARBORPHONE 25Six tubes; 3 t.r.f. (01-A), detector (01-A), 2 audio(01-A and 71). One control. Volume control: rheostat.Shielded. Battery cable. Output device. C-battery connections.Loftin-White circuit. Antenna: 75 feet. Panel:7} x 15 inches, metal. Prices: Model 25, table, $125;Model 252, $185; Model 253, $250; Model 255, combinationphonograph and radio, $600.NO. 527. ARBORPHONE 27Five tubes; 2 t.r.f. (01-A), detector (01-A), 2 audio(01-A). Two controls. Volume control: rheostat. C-battery connections. Binding posts. Antenna: 75 feet.Prices: Model 27, $65; Model 271, $99.50; Model 272,$125.NO. 528. THE "CHIEF"Seven tubes; six 01-A tubes and one power tube.One control. Volume control: rheostat. C-battery connection.Partial shielding. Binding posts. Antennaoutside. Cabinet size: 40 x 22 x 16 inches. Prices:Complete with A power supply, $250; without accessories,$150.NO. 529. DIAMOND SPECIAL, SUPER SPECIAL,AND BABY GRAND CONSOLESix tubes; allJOl-A type. One control. Partial shielding.C-battery connections. Volume control: rheostat.Binding posts. Antenna: outdoor. Prices: DiamondSpecial, $75; Super Special, $65; Baby Grand Console,$110.

RADIO BROADCAST ADVERTISER 405Universally UsedbyAmateur Builders fe Adopted byJM.Leading SetM'fgrs.-, -First Choice"of ProfessionalBuildersEndorsed byForemost RadioEnqineefS~Sold Everywhereby Leading DealersFIRST CHOICEof the Keenest Minds in Radio IDurham standard resistors are made in ranges from 500ohms to 10 megohms Durham Powerohms for "B"Eliminators and Amplifier circuits are made in 2.5 wattand 5 watt sizes in ranges from 500 to 100,000 ohms.FIRSTAdopted by Leading Radio ManufacturersPhilcoFansteel Products Co.Kellogg-SwitchboardWestern ElectricF. A. D. AndreaSterling Mfg. Co.Kokomo ElectricGarod Radio Corp.Browning-DrakeHoward RadioRESISTORA-C DaytonSCHOICE because Durham was the first and original"metallized filament" resistor because years ofheavy production and the confidence of leading radio manufacturershave given us time to produce a perfect product.Durham Resistors and Powerohms are the leaders in theirfield because their uniform, unfailing accuracy and absolutereliability have been proved time and time again.This iswhy they are the first choice of foremost engineers,leading manufacturers, professional set builders andinformed radio fans who demand quality results.Like Durham Resistorsare also the leaders in their field. Theand Powerohms, Durham ResistorMountingsonly upright mountings made; takes minimum spacemade of high resistance moulded insulation best qualitytension -spring bronze contacts. Single and double sizes.METALLIZEDINTERNATIONAL RESISTANCE CO., Dept. D, 2% South 20th Street,POWEROHMSPhiladelphia, Pa.

406 RADIO BROADCAST ADVERTISERNO. 530. KOLSTER, 7A AND 7BNO 433. ARBORPHONESeven tubes; 4 t.r.f. (01-A), detector (01-A), 2 audio Five tubes; 2 t.r.f., detector, 2 transformer audio.(01-A and 12). One control. Volume control: rheostat All 01-A tubes. Two dials. Plate current: 16mA. Volumecontrol: rheostat in r.f. and resistance in r.f. plate.on r.f. Shielded. Battery cable. C-battery connections.Antenna: 50 to 75 feet. Prices: Model 7A, $125; Model C-battery connections. Binding posts. Antenna: taps7B, with built-in loud speaker, $140.for various lengths. Cabinet size: 24 x 9 x 10J inches.Price: $65.NO. 531. KOLSTER, 8A, SB, AND 8CEight tubes; 4 t.r.f. (01-A), detector (01-A), 3 audioNO. 431. AUDIOLA 6(two 01-A and one 12). One control. Volume control:Six tubes; 3 t.r.f. (01-A), detector (00-A), 2 transformeraudiorheostat on r.f. Shielded. Battery cable. C-battery connections.Model 8A uses 50 to 75 foot antenna; model(01-A and 71). Drum control. Plate current:20 mA. Volume control: resistance in r.f. plate.8B contains output device and uses antenna or detachableloop; Model 8C contains output device and usesStage shielding. Battery cable. C-battery connection.Antenna: 50 to 100 feet. Cabinet size: 28-J x 11 x 145antenna or built-in loop. Prices: 8A, $185; 8B, $235; inches. Price not established.8C, $375.NO. 532. KOLSTER, 6D, 6G, AND 6HNO. 432. AUDIOLA 8Six tubes; 3 t.r.f. (01-A), detector (01-A), 2 audio Eight tubes; 4 t.r.f. (01-A), detector (00-A), 1 transformeraudio (01-A), push-pull audio (12 or 71). Bridge(01-A and 12). One control. Volume control: rheostaton r.f. C-battery connections. Battery cable. Antenna: balanced t.r.f. Drum control. Volume control: resistance50 to 75 feet. Model 6G contains output device and inbuilt-in loud speaker; Model 6H contains built-in Br.f. plate. Stage shielding. Battery cable. C-batteryconnections. Antenna: 10 to 100 feet. Cabinet size:power unit and loud speaker. Prices: Model 6D, $80; 285 x 11 x 149 inches. Price not established.Model 6G, $165; Model 6H, $265.NO. 542 RADIOLA 16NO. 533. SIMPLEX, SR 9 AND SR 10Five tubes; 3 t. r. f. (Ol-A), detector (Ol-A), 2 transformeraudio (01-A and 112). One control. C-batteryFive tubes; 2 t.r.f. (01-A), detector (00-A), 2 audio(01-A and 12). SR 9, three controls; SR 10, two controls.Volume control: rheostat. C-battery connections. size: 16V2 x &/, x 7V2 inches. Price: $69.50 without ac-connections. Battery cable. Antenna: outside. CabinetBattery cable. Headphone connection. Prices: SR cessories.9,table, $65; consolette, $95; console, $145. SR 10, tableNO. 456. RADIOLA 20$70; consolette, $95; console, $145.Five tubes: 2 t.r.f. (99), detector (99), 2 transformeraudioNO. 534. SIMPLEX, SR (99 and 20). Balanced t.r.f. and regenerative detector.Two dials. Volume control: regenerative.11Six tubes; 3 t.r.f. (01-A), detector (00-A), 2 audio Shielded. C-battery connections. Headphone connections.Antenna: 75 to 150 feet. Cabinet size: 19$ x(01-A and 12). One control. Volume control: rheostat.C-battery connections. Battery cable. Antenna: 100 11J x 16 inches. Price $115 including all tubes.feet. Prices: table, $70; consolette, $95; console, $145.NO. 457 RADIOLA 25NO. 535. STANDARDYNE, MODEL S 27Six tubes; five type 99 and one type 20. Drum control.Super-heterodyne circuit. C-battery connections.Six tubes; 2 t.r.f. (01-A), detector (01-A), 2 audio(power tubes). One control. Volume control: rheostatBatteryon r.f. C-battery connections. Binding posts. Antenna:cable. Headphone connections. Antenna: loop.Set may be operated from batteries or from power mains75 feet. Cabinet size: 9 x 9 x 191 inches. Prices: S 27, when used with model 104 loud speaker. Price; $165$49.50; S 950, console, with built-in loud speaker, with tubes, for battery operation. Apparatus for operationof set from the power mains can be purchased$99.50; S 600, console with built-in loud speaker,$104.50.separately.NO. 481. PFANSTIEHL 32 AND 322NO. 493. SONORA FSeven tubes: 3 t.r.f. (01-A), detector (01-A), 3 audio Seven tubes; 4 t.r.f. (01-A), detector (00-A), 2 transiormeraudio (01-A and 71). Special balanced t.r.f.(01-A and 71). One dial. Plate current: 23 to 32 mA.Volume control: resistance in r. f. plate. Shielded Two dials. Plate current: 45 mA. Volume control:Battery cable. C-battery connections. Output device. rheostat in r.f. Shielded. Battery cable. C-batteryAntenna: outside. Panel: 17f x 85 inches. Prices: No. connections. Output device. Antenna: loop. Console32 cabinet, $145; No. 322 console, $245 including si/e: 32 x 45! x 17 inches. Prices range from $350 toloud speaker. $450 including loop and loud speaker.NO. 494.SONORA ESix tubes; 3 t.r.f. (01- A), detector fOO-A), 2 transformeraudio (01-A and 71). Special balanced t.r.f.Two dials. Plate current: 35 to 40 mA. Volume control:rheostat on r.f. Shielded. Battery cable. C-batteryconnections. Antenna: outside. Cabinet size: varies.Prices: table, $110; semi-console, $140; console, $240including loud speaker.NO. 495.SONORA DSame as No. 494 except arrangement of tubes; 2t.r.f., detector, 3 audio. Prices: table, $125; standardconsole, $185; "DeLuxe" console, $225.NO. 482. STEWART-WARNER 705 AND 710Six tubes; 3 t.r.f., detector, 2 transformer audio.All 01-A tubes. Balanced t.r.f. Two dials. Plate current:10 to 25 mA. Volume control: resistance in r.f.plate. Shielded. Battery cable. C-battery connections.Antenna: 80 feet. Cabinet sizes: No. 705 table, 26ix 11{ x 13j inches; No. 710 console. 29J x 42 x 17Jinches. Tentative prices: No. 705, $115; No. 710$265 including loud speaker.NO. 483. STEWART-WARNER 525 AND 520Same as No. 482 except no shielding. Cabinet sizes:No. 525 table. 19 J x 10 x 11} inches; No. 520 console,228 x 40 x 14 M inches. Tentative prices: No. 525, $75;No. 520, $117.50 including loud speaker.NO. 459. STROMBERG-CARLSON 501 AND 502Five tubes; 2 t.r.f. (01-A), detector (00-A), 2 transformeraudio (01-A and 71). Neutrodyne. Two dials.Plate current: 25 to 35 mA. Volume control: rheostaton 1st r.f. Shielded. Battery cable. C-battery connections.Headphone connections. Output device. Panelvoltmeter. Antenna: 60 to 100 feet. Cabinet sizes:No. 501, 25J x 13 x 14 inches; No. 502, 28 )?, x 50ft x 16J inches. Prices: No. 501, $180; No. 502, $290.NO. 460. STROMBERG-CARLSON 601 AND 602Six tubes. Same as No. 549 except for extra t.r.f.stage. Cabinet sizes: No. 601, 27i^ x 16-J x 14 fe inches;No. 602, 28f x 51J x 19| inches. Prices: No. 601, $225;No. 602, $330.NO. 486. VALLEY 71Seven tubes; 4 t.r.f. (01-A), detector (01-A), 2 transformeraudio (01-A and 71). One dial. Plate current:35 mA. Volume control: rheostat on r.f. Partiallyshielded. Battery cable. C-battery connections. Headphoneconnection. Antenna: 50 to 100 feet. Cabinetsize: 27 x 6 x 7 inches. Price $95.NO. 472.VOLOTONE VIIISix tubes. Same as No. 471 with following exceptions;2 t.r.f. stages. Three dials. Plate current: 20mA. Cabinet size: 265 x 8 x 12 inches. Price $140.roue*-. -^*T|) It feril anelisteners-in want crystal clear, undistorted tonesmore than distance.They seem to want to set their dials for a desired programand get it right to get it full, strong and free from theannoyance of blurring and what might be termed "warped "tones.The one big thing that Carborundum Stabilizing DetectorUnit does in any set is to improve the tone quality. Besidesyou will find that it increases the volume and gives yougreater distance if you want it..TULH1Beg.u.s.p.t.off.CLARIFIES RECEPTIONDo will v^apbonuuao.iLim Cjrria. JL/eats amo. ResistorsSend for Hook-Up Book D-2''The' CarborundumCompanyNiagara Falls, N.Y.Please send freeHook-Up Book D-2THE CARBORUNDUM COMPANY, NIAGARA FALLS, N. Y.SALES OFFICES AND WAREHOUSES IN New York, Chicago, Boston, Philadelphia, Cleveland, Detroit, Cincinnati / ClryPittsburgh, Milwaukee, Grand Rapids /'The Carborundum Company, Ltd., Manchester, Eng.StatestreetZ1JIC

$2.00RADIO BROADCAST ADVERTISER 407Sickles Coil Set No.lgAfor Roberts CircuitSICKLESDiamond - Weave Coilsnew Sickles Shielded Tuned RadioTHE Transformer prevents both outsideand local interference. It is remarkablycompact, sharp tuning, sturdy.Sickles Diamond-weave coils have establishedan enviable reputation for lowdistributed capacity, low dielectric losses,and large range of frequency with smallvariable capacity.The ideal coil for the Naald LocalizedControl Tuning Unit and for the TruphonicCatacomb Assembly.Why all this stuffJbr an aerialThere are Sickles Diamond Weave Coilsfor all Leading Circuits,The F. W. SicklesCo.132 Union StreetSPRINGFIELD, MASS.COIL PRICESNo. 30 Shielded Transformer .eachNo. 24 Browning-Drake 7.SO SetNo. ISA Roberts Circuit "8.00No. 25 Aristocrat Circuit 8.00 "_ VsysS. _ ,BALDWINLOUD SPEAKERSFamous'"Benj. Franklin once said:"My performance devotes itaelfentirely to thy service and willserve thf-e faithfully and if ithas the good fortune to pleaseits master, tig gratification"enough for the lator ofPoor RichardBmW3Jis without comparison, due to the superfinequality of its unit. To-day, as15 years ago, Baldwin performance isstill the standard by which others arejudged, comparable to the sensitivemechanism of a fine watch. The NewBaldwin "99" can be used on any set.Ask your deafer todemonstrate it.At allGood DealersWrite For Booklets-BALDWIN UNITS-Loudspeaker units.Phono adapters, andhead sets are standardthe world over.J. W. & W. L. WOOLFDistributors and Exporters ForNATHANIEL BALDWIN, Inc.227-229 Fulton St. New Yorkwhen allyon needis this "The trouble and expense of erecting an outdoorantenna are now absolutely unnecessary. TheDubilier Light Socket Aerial has taken the placeof loose wires, crazy poles, lightning arresters andall the other accessories of an old-fashioned antenna.Full volume isguaranteed. So is clarity and distance. You'll find, toothat this remarkable device greatly reduces both static and interference.Convince yourself without risk all dealers sell the Dubilier Light SocketAerial on a 5-day money-back basis.DubilierApproved Blocksfor Power UnitsIf you're building anA-B-C eliminator, insiston the high factor ofsafety found only in theapproved Duhilier condenserblocks. Raytheonand all standard circuitsprovided for.Price #1.50The AccurateDubilierMetaleakDon't underestimate the importanceof accurate and quiet tubularleaks in the performance of yourreceiver. Metaleak is smaller thanmost, but interchangeable on anystandard mounting. All resistances40c to 65c.DUBILIER CONDENSERCORPORATION4377 Bronx Blvd. New YorkYou'll like the newDubilier MicadonAnewshape and moulded Bakehtecase have made the "StandardFixed Condenser of Radio"a better and better -lookingMicadon. Fully protected frominjury and outside capacity.Terminals adapted to screwedor soldered connections.Prices 45c to #1.50Condensers

408 RADIO BROADCAST ADVERTISERMore than IfiOO^OOO owners ofGeneral ElectricBattery Chargersnow havepepgyradio batteries - alwaysGETYBORS//2o,,UICKDon't wait! Send today for this wonderful book.See how 14,000 live radio dealers make biggerprofits by buying from The Harry Alter Company,America's foremost wholesalers of receiving sets,kits, parts and accessories the largest stock ofstandard, nationally advertised radio goods carriedanywhere.RADIO'SGREATEST CATALOGCompare its low prices with those of any othercatalog. You will be amazed. Note: We sell only toradio retailers. Write for your copy NOW.5-AmpereTungarG-E TrickleChargerhel$arry Ulter Co1754 Michigan Avenue CHICAGOKeep your radio set ready at all times for all the goodthings that come over.Just turn on Tungar (the name ol the General Electric batterycharger) at ference. It cannot blow outTungar causes no radio Inter*night, leave it as you would the light in thehall .... in the morning your storage batteries are tubes.peppedAnup and overnight charge costs aready for active dutydime.More than 1,000,000 G-E Tungars are in use today. For the It is a G-E product developedin the Research Labora-Tungar long ago established its reputation for dependable,tories of General Electric.trouble-free, economical service.The 2- or S-ampere TungarsYour dealer can help you. Ask him to show you the popular charge 2-, 4-, and 6-volt"A"2-ampere Tungar that gives both trickle and boost chargingbatteries, 24- to 96-volt "B"batteries inrates. It charges "A" and "B" series; and autoradio batteries and autobatteries, too. No extra attachmentsneeded.batteries, too.New Low Prices(East of the Rockies)2-ampereTun par, now $ 145-ampereTungar, now $24G-E Trickle Charger, now$10!BATTERY ~CHARG ErT|DepartmentTungar a registered trademarkGeneral Electricis found onlyCompanyon the genuine. Look for it on the name plate. Bridgeport, ConnecticutGENERALThis hard, glassy enamel has the samerate of expansion as the porcelaintube and the resistance wirethat is wound on it. Consequentlythe Resistor may b** operatedat high temperatures with-damaging it.outNEW VITREOUSENAMEL RESISTORSThese Resistors are wire-wound andcoated with a vitreous enamel winchprotects the wire from mechanical injuryand oxidation.These Resistors are guaranteed permanentlyaccurate within 5 per cent, of rated value.Resistors from 750 to 20,000 ohms, two types2 in. long, dissipating 20 watts; 4 in. long,dissipating 40 watts.In Canada: Carter Radio Co., Ltd., TorontoOffices in principal cities of the worldarter Radio OMODERNIZE YOUR RADIO!UILD your own Battery-Less receiver with the ADVANCED 1928 MODEL SOVEREIGN A-C KIT.No more A Battery No A Batterv Eliminator No Hum No Michrophonic Disturbance JUSTCLEAR CLEAN CUT TRUTHFUL REPRODUCTION powered from the never failing light socketby the mere snap of the switch.CONVERT YOUR PRESENT RECEIVER TO 1928 STANDARDSWITH THE ADVANCED 1928 MODEL SOVEREIGN A. C. KITwith but slight modifications, easily accomplished by following the detailed instructions supplied in each Sovereign A.C.Kit ANY CIRCUIT becomes light socket powered receiver.You need not be a Radio Engineer or master "radiotrician" to construct an A. C. Receiver or convert your presentset. Just follow the very simple, definite, detailed instructions given FREE w!th Sovereign Equipment. That's all!When you purchase Sovereign Products you have the knowledge that nothing in the ratho industry today carriesgreater assurance of proper design construction satisfaction or guarantee.Sovereign A. C. Tubes acknowledged the "Crowning as they are non-michrophonic. it all inSummingAchievement" in the Radio Tube Field are unconditionally words. Sovereign Equipment means ECXJNOMYfewEF-aguaranteed. They have more rugeed construction a FICIENCY MINIMUM SERVICING THE IDEALlonger life! Sovereign A-C Tubes improve tonal quality IN RADIO RECEPTIONIf your dealer cannot supply you, we will ship direct to you C.O.D. Sovereignbe furnished for use on no or 220 Volts 25 or 60 Cycles.A-C Kit canSOVEREIGN A-C Kit no or 220 Volts 60 Cycles. Price $8.75SOVEREIGN A-C Kit no or 220 Volts 25 Cycles. Price ^.7^In ordering Kits specify Voltage of House Current No. of Cycles Type of CircuitNo. of Tubes.SOVEREIGN A-C TUBESPrice Ji?.ooSOVEREIGN A-C POWER TUBES FOR LAST AIT.IO STAGE Price $6.00We have prepared for you a comprehensive NON-TECHNICAL pamphlet on A-C Receivers and Tubes. Write foryour copy today!SOVEREIGN ELECTRIC & MANUFACTURING CO.12 No. Sangamon Street Chicago Illinois

RADIO BROADCAST ADVERTISER 409In Trouble ? ?Has a moisture permeated bypass condenserruined your receiver or amplifier ?A defective bypass condenser or couplingcondenser in a receiver or amplifier marsreception causes distortion.Insure against such troubles use the latestAEROVOX development an AEROVOXbypass condenser sealed in a Bakelite casenon - inductively wound impervious tomoisture its electrical condition is as goodafter a year as the day it was installed.Made in all capacities up to 1 mfd andrated at 200 volts D C working voltage.Bui'//'Btlttr"70 Washington St., Brooklyn, N. Y.FROST-RADIODE LUXEAPPARATUSnow Is available at your favorite dealer's. Thesenew De Luxe items of Frost -Radio include Rheostats.Potentiometers and Variable High ResistanceUnits, with and without switch. Gem Rheostatsand Fixed Resistances, all in a wide range ofresistance windings. You'll like them find themdependable, high in quality and fairly priced.FROST-RADIOS-i8io De Luxe 10 ohm Bakclitc CnmbinationRheostat ami Battery Switch, $J.$5HERBERT H. FROST,'-Main Offices and FactoryEL.KHART, IND.Adjustable "B" Voltagesin any combinationfrom to 180also adjustable "C"Type 445Plate SupplyPrice $55UX-280 or CX-380Rectifier Tube forabove, $5Type 445PlateSupplycomplete withTube, $60Voltage from to 50TheNewGENERAL RADIOPLATE SUPPLYEmbodying new and distinctive features in plate supply design1 . A djustable wire wound resistance -with sliding taps which control voltagesso that any combination of voltages from o to 180 may be taken from thefour positive "B" terminals. This method of voltage control is superiorto the use of several resistances with exterior knob controls. It has theadvantage that once the sliding taps are adjusted to the proper operatingvoltages of the tubes, they are tightened in place by thumb screws andvoltages will remain constant, but are immediately available for readjustmentwhenever the unit is used with a different set.2. Adjustable "C" voltage for power tube3. High voltage test condensers in filter circuit4. Uses UX-z8o or CX-jSo rectifier tube which has maximum output of100 milliamperes, thereby providing sufficient current for sets of themulti-tube type.5. Automatic cut-out switch breaks the no vclt A. C. circuit when coveris removed for adjusting voltages or connecting wires to taps, therebymaking unit absolutely safe even in the hands of persons not familiarwith electrical apparatus.6. Designed to meet specifications adopted by the National Board of FireUnderwriters.7. Absolutely guaranteed against mechanical and electrical defect uponleaving the General Radio factory.Cost, which has been a secondary consideration to over-all efficiency hasbeen kept as low as peak performance and production economies permit.Price from your dealer, or direct from the factory if your dealer cainnil supply youType 445 Plate Supply Unit $55.00Type UX-280 or CX-380 Rectifier Tube for above $5.00Licensed by the Radio Corporation of America only for Radio Amateur, Experimentaland Broadcast Reception.Under terms of R. C. A. license unit may only be sold with tube.GENERAL RADIO COMPANY CAMBRIDGE, MASS.

410 RADIO BROADCAST ADVERTISERInstallationsSafeRadio's Best WireCORWICO "FLEXIBUS"HOOK-UP WIRE"Corwico" F 1 e x i b u s(Solid or Stranded) isa flexible insulated tinnedcopper hook-upwire which makes a neatand efficient product for*'point to point" andsub-panel wiring. It iscovered with a varnishedcambric flame proofinsulation finished inred, green, yellow,brown or black."From The Ground Up"No chain is stronger than its weakest link. That's whythe wire you use in your radio set or the wire that isused in the set you buy, is an important factor. Whytake a chance, when for the same price and in manycases less, you can have the best by specifying "Corwico"radio wires. Their superior merits and all-around efficiencyhave been proven by amateurs, experts and radioreceiving set manufacturers everywhere.The next time you need wire for any radio purpose, askyour dealer for "Corwico." If he can't supply you,write us direct."Corwico" Radio WiresAntenna WireHook-up Wire(Solid, Stranded and braided) Lead-in WireComplete Aerial KitsAnnunciator WireMagnet Wire Loop Aerial WireBattery CableLitz WireBus Bar WireFlexible Wire"Convico'* Radio Wires are sold by all leading dealers.Write for free booklet on radio wires and their uses.CORNISH WIRE COMPANY30 Church Street New York City"'Superior to all others tested"Recognized radio engineers have for a long time knownthe excellence of Tobe Condensers. They have thequality of continuing to function perfectly over longperiods of time. Now the Tobe No. 662 high voltageB Block has been selected exclusively by McMurdoSilver for use with the new Silver-Marshall UNIPACand Mr. Silver has written us the above reproducedletter. Send for price list B-io.Tobe Deutschmann Co,S Cambridge- - Mass.Safety Provisions Specified bythe Board of Fire Underwritersin Making Antenna InstallationsThe Lightning HazardDanger From Power LinesBy EDGAR H. FELIXAN ONCOMING bolt of lightning neverstops to argue. It has only one thing inmind an incredible hurry to reachMother Earth. Your little, puny pound ofcopper antenna wire, strung up a few feet abovethe surface of the earth, has no more influence inattracting a bolt of lightning than a mosquitohas to entice you to a symphony concert. Iflightning ever strikes your antenna, it is merelya coincidence. The presence or absence of anantenna on a building has nothing to do witheither the attraction or repulsion of lightning.There is in the atmosphere at all times, butmore especially during the summer months, acertain amount of static electricity present.Any body of metal or wire tends to collect thisatmospheric electricity if it is not connectedto ground, and the electrical potentials built upmay become of dangerous proportions. Alightning arrester provides an easy path toground for these charges which tend to accumulateon the antenna, but is so constructed that itdoes not afford a path to ground for the radiosignals. When there is a thunder-shower in theimmediate vicinity, the potentials induced in theantenna are greater than at other times, andalmost continuous discharges take place throughthe arrester to ground.With a lightning arrester properly installed,there seems to be very little danger from thisatmospheric electricity, or induced currentsfrom near-by electrical disturbances. To supportthe contention, let us consider the evidence ofexperts. Victor H. Tousley, Chief of ElectricalInspectors in the Chicago District, reports thatof the 34 cases where the Chicago Fire Departmentwas called out in response to a fire causedby lightning, only 12 of the buildings had antennas;and, in only four of these was there anyevidence that lightning had followed the antennawire to the ground.William S. Boyd, an electrical engineer ofChicago, has, for some years, been compilingstatistics regarding fires caused by lightningstriking radio installations. His report listsonly 15 damaged by lightning during the years1922 to 1924 not a very formidable figure.Six of these accidental "hits" damaged only theantenna because the lightning arrester did itswork effectively.In the entire district of Philadephia, there is arecord of only one fire caused by lightningstriking a radio antenna, according to an officerof the Fire Underwriters' Association in thatcity. The antenna and lightning arrester weredestroyed, but no damage was done to the receivingset.Another hazard, which depends purely on thematter of placement of the antenna and goodworkmanship in putting it up, is the likelihoodof the antenna coming into contact with electricalwires, either low tension or high tension.The most important provisions, formulated by(Continued on page 412)

. .RADIO BROADCAST ADVERTISER 411New!No More Socket TroubleA socket's only job is to provide a perfectcontact. The New Eby Socket has a 3 pointwiping spring contact the full length of theprong, the most scientifically perfect typeknown. The prongs are completely enclosedand fitsnugly against the phenolic walls ofthe socket they can't spread.With the New Eby Socket your sockettroubles are gone. Easy to mount above orbelow Bakelite, Wood or Metal.Specified in most of the leading popularcircuits.List Price 40cTHE H. H. EBY MFG. Co.INCORPORATED4710 Stenton Ave.Phila., Pa.Makers of Eby Binding PostsEARNS$5OO.In HisThat's the record of Member Lyle Follick,Lansing Mich. Member Werner Eichler,Rochester, N. Y. writes, "I have madeover #50. a week in my spare time"With its proven money making plans, advice, cooperationin furnishing parts at wholesale and training,the Radio Association of America is helping itsmembers start radio stores, secure better positions,increase their salaries, earn $3. an hour upwards inspare time building sets and serving as radio"doctors."Join the Association without delay, because we havea plan whereby yourmembership may not need notcost you a cent. Only a limited number of thesememberships are acceptable. Write before it's toolate.RADIO ASSOCIATION OF AMERICADept. RB-10 4513 Ravenswood Ave., ChicagoSend me your book and details of your SpecialMembership Plan.Name .dddrtss .City .... . StateTRADE MARKMAGNIFICENT TONE-SUPER SELECTIVE-POWERFUL DISTANCE GETTER \America's big, old, reliable Radio Corporation*(8th successful year) guarantees itsbig, powerful, latest 6, 7 and 8 tube Miracosets to give "the finest, most enjoyable performanceobtainable in high grade radios."Unless 30 days' use in your home fullysatisfies you and everybody who hears itthat a Miraco is unbeatable at any pricefor beautiful, clear cathedral tone, razoredgeselectivity, powerful distance reception,easy operation, etc. don't buy it!Your verdict final absolutely no stringsto this. Save or make lots of money onsets and equipment by writing for testimonyof nearby users and Amazing SpecialFactory Offer.Run from "AC" Current or BatteriesMiraco's work equally fine on electric housecurrent or with batteries. Take your choice.Many thousands of Miraco users whobought after thorough comparisons testifythey enjoy programs Coast to Coast,Canada to Mexico, loud and clear withthe magnificent cathedral tone quality ofcostliest sets. Don't comfuse Miraco's withcheap, "squawky" radios. Miraco's havefinest parts, latest approved shielding,metal chassis, etc. as used in $200 sets.i6 tubeSuper*MIDWEST RADIO CORP.Cincinnati, Ohio[BEAUTIFULLY ILLUSTRATED>efmil coupon30 DayiTr'alL- or Battery Set/Deal Direct with Big Reliable MakersYour Miraco reaches you completely assembled, rigidlytested, fully guaranteed. Easy to connect and operate.30 days free trial. 3 year guarantee if you buy. Choiceof beautiful consoles {with latest built-in orthophonictype speakers having 8 feet ot tone travel] and tablecabinets, also offered. You take no risk, you insure satisfaction,you enjoy rock-bottom money-saving-prices bydealing direct with one of radio's oldest, most successfulbuilders of fine sets.MIRACO "Powerplus" DCM> ,bothin8and7tubemodelshavemagnificently beautiful,clearcathedral tone quality. Turnone dial for stations everywhere.Ultra -selective. Miraco multi-Btage distance amplifi cation gives''power-plus' 'on far-orTstationa.Latest all-metal shielded chassis.Illuminated dial. Fully guaranteed.Try one free for SO daysfiChoice of beautiful cabinets.E lect r ify Any RadioMIDWEST NO-BATTERYPower UnitsM A"."B"and"C*power, direct fromlight socket, withoutbatteries!WriteforMidweetpricesnd discount*. Midweat Unit* are biffbattfrmd* Inntinsly dependable, quiet in up*ratioD,full ffuamiteed.MIDWEST RADIO CORPORATIONPioneer Builders of Sets406-C Miraco Building, Cincinnati, Ohio.IItfstoone dial,METAL SHIELDED/.CHASSIS14975!RETAl L LIST]COUPONNOTORDERft Without obligation, s,-iid free catalog, AMAZING SPECIAL WHOLESALEPRICE OFFER, testimony of nearby Miraco users.INAMEADDRESS

(|412 RADIO BROADCAST ADVERTISERA "Million-Dollar" FrontFor Your ReceiverFRONTVIEWwaited to produceHAMMARLUND a drum dial that would make thesingle-control of tuning condensers reallyThe NewHAMMARLUNDIlluminatedDrum DialAn up-to-the-minute tuningimprovement every setbuilderwill want to install.practicable.Local stations can now be tuned in over theentire wave band by the simple movementof two fingers. Distant stations, requiringa finer adjustment, are brought in by aslight realignment of the individual halvesof the dial.Viewed from the front, the new HammarlundDrum Dial gives to any receiver adelightful, professional finish. The bronzeescutcheon plate, richly embossed and oxidized,endows the panel with a classicbeauty.BACK VIEWMechanicalFeaturesOver-size die-cast frame ;Bakelite drums, withknurled edges ;translucentcelluloid wavelengthscales, illuminated by asmall electric light, withhandy switch, connectingwith the "A" Battery circuit.Adaptable to allstandard panel proportions.HAMMARLUND MANUFACTURING COMPANY424-438 W. 33rd Street, New YorkItammarlund3o*o SfiitoK. T^jctdLu-VAlready many leading radiodesigners have officiallyspecified HammarlundPrecision ProductsF> TC ISfor^|IONtheir latest circuits. B -HI f~ . .. ^~^v 1 v I I X^- T~ ^^BIGRAOIO CATALOGFrom the "Big, FriendlyNEWRadio House"1928 Book offers finest,newest well-known sets; parts,eliminators, accessories at lowestprices. Set-builiiers.dealers,aRent8WRITE for this CATALOG !ifestemBadioMfgCo.134 West Lake St. Dept. 47CHICAGO, ILL.PRODUCTSDealer inquiries invitedconcerning several othernew and appealing Hammarlunddevelopments thaving a wide sales apfeal.RADIO PANELSBAKELITEHARD RUBBERCut, drilled and engraved to order. Send rough sketchfor estimate. Our complete Cataloe on Panels, Tubes andRods :ill of genuine l..,keiitc or Hard Rubber mailedon request.STARRETT MFG. CO.521 S. Green Street Chicago, 111.Late8tadvanced circuit. AHeteel chassis totally shielded.Balanced parts of best quality.Marvelous power and selectivity. Getatbe long ranee stations as clear as a bell.One dial single control. An unsurpassed valujust inic t>f uur many mighty bargains.FREE Log ana Call BookandBlgNwCtloB-justoffthepresa. Pull ofRatliu Bantains. Send for your free copy nuwlAmerican Auto & Radio Mfg. Co.HRY ScWART7,BKKG, Prea.Dept. 122 American Radio Bldn.. Kansas City. MaSafe Radiothe Board of Underwriters, are abstracted asfollows:PERTAINING TO THE LIGHTNINGHAZARD1. LIGHTNING ARRESTER. Each lead-inwire shall be equipped with an approved lightningarrester, operative when 500 volts or moreare impressed on it, and connected to a groundeither inside or outside the building, as near tothe arrester as possible. The arrester shouldnot be installed near any inflammable material.If a grounding switch is used, it should shunt thearrester, and should have a capacity of 30 amperesat 250 volts.2. APPROVED GROUNDS. The ground usedispreferably made to a cold-water pipe, wheresuch a pipe is available and is in service andconnected to the street mains. Other permissiblegrounds are: the grounded steel frames ofbuildings, the grounded metal work in the building,and artificial grounds such as driven pipes,rods, plates, cones, etc. Gas pipe shall not beused for a ground. The ground should be installedso as to be safe from mechanical injury.An approved ground clamp should be used forconnecting the wires, and the pipe should bethoroughly cleaned.3. GROUND WIRE. The protective groundingconductor may be of bare or insulated wiremade of copper, bronze, or approved copper-cladsteel. The ground wire shall in no case be lessin current-carrying capacity than the lead-inwire, and in no case shall it be smaller than No.14 if copper, nor smaller than No. 17 if of bronzeor copper-clad steel. The ground wire shouldbe run in as straight a line as possible from theprotective device to the ground connection. Insidewiring should be fastened in a workmanlikemanner and should not come closer than twoinches to electric conductors, unless porcelaintubing forms a permanent separation fromsuch conductors. This last applies to all insidewires.7.FUSES IN GROUND LEADS. No fuses shallbe used in any lead-in conductors or in the groundREQUIREMENTS FOR PROTECTION FROM HIGHVOLTAGE8. INSTALLATION NEAR HIGH VOLTAGEMAINS. The antenna and counterpoise, outsidethe building, shall be kept well away fromany wires carrying a potential of 600 volts ormore, including railway, trolley, or feeder wires,in order to avoid accidental contact. Thesevoltages are sufficient to cause shock dangerousto life and to cause fires. Antenna installationsnear electrical wires of less than 600 volts potentialmust be installed in a durable mannerand shall be provided with suitable clearancesso that there is no possible chance of accidentalcontact, due to sagging or swinging.9. SPLICES IN ANTENNA WIRE. Splicingin antenna or lead-in wires should be solderedunless made with an approved splicing device.10. LEAD-IN CONDUCTORS. Lead-in conductorsshall be of approved copper-clad steel orother metal which does not corrode excessively,;of no smaller gauge than No 14, unless approvedcopper-clad steel is used when the gauge may beNo. 17.11. LEAD-IN CONDUCTORS OUTSIDE THEBUILDING. The lead-in conductor shall notcome closer than four inches to any electriclight or power wires unless separated therefromby a porcelain tube or other firmly fixed nonconductor.12. LEAD-IN INSULATOR. An approvedlead-in insulator should be used.13.STORAGE BATTERY CIRCUIT. An importantand new provision rarely obeyed is thelrequirement that fuses of not less than 15-amperes capacity shall be installed and locatedpreferably at or near to the battery. An approvedcircuit breaker of the same minimumcapacity may be used. The leads from the batteryto the receiver shall consist of conductorshaving approved rubber insulation.Clearly, these rules are simple and easily com-(Continued on page .// /)

RADIO BROADCAST ADVERTISER 413All-Metal CabinetFor 1927-28 Hook-Ups!Model 250For A. C. orBattery SetsUsing7x187x218x188x21PanelsPric. $1.75Inside dimensions 25"xl4%"x9Vg". Hinged top with stay joint. Rigidly formed forstrength and appearance. Felt foot rest rubber lid stops. A welded job doing awaywith troubles of swelling, shrinking, cracl::ng, splitting and uncertain fit.Best tubes-Best receptionThe original beauty of natural wood grainscombined with the efficiency of all metalconstruction !By our photo litho process, wereproduce mahogany and walnut hardwood,and novelty finishes, so gorgeous in their conseptionthat they excite the admiration of allwho see it.Spacious interior dimensions are demandedfor housing all the latest hook-ups! Vee Deemetal cabinets are designed for that purpose.909oofall the 1927-1928 hook-ups are coveredby the dimensions of Vee Dee No. 250cabinet illustrated above. Beautiful practical!Low price!New broadcast developmentsmake itnecessary tohave the latest types of tubesfor fullest enjoyment of yourreceiving set.Bring it up to date with acomplete installation of thenew Gold Seal radio tubesspecially developed for modernreception. You will bedelighted with the improvement.You can make the changesyourself no trouble. Ournew booklet'tells you allabout it. Send today for yourcopy it is free. Use couponbelow.All Standard TypesMetal Panel for Citizens Super EightConstructed in accordance withCitizens Radio Call Book andtime*.*S. C. 2 Assembly UnitComplete Panel, Chassis, 7x18, fully drilled. Beautifulwood grain finish, handsomely decorated. Kit includesall necessary bushings, washers and hardware accessories.McMurdo Silver, Rernler, Cock-*aday co-ordinated designingMetal Panel and Chassis for Silver-Marshall1927 Model"^ Super-HeterodyneComplete assembly consisting of panel and chassis,fully drilled, beautiful wood finish with special twocolordecoration, all fibre bushings and washers included,also screws, bolts and hardware accessories.IIIIGold Seal Electrical Co.250 Park Ave., New YorkSend me copy of the new booklet.NameIUnipac HousingEspecially designed and provided for Silver-MarshallPower Hook-ups including cabinet and chassis, drilledand with all small hardware.IIAddress!i^Metal Panels and Chassis in All Standard SizesJOBBERS, DEALERSWRITE FOR PRICESGold SealRadio Tubes tSet Buildersif your dealer cannot supply you, write directThe Van Doom Company160 North La Salle StreetFactory. Qttincy, IllinoisChicago, Illinois

414 RADIO BROADCAST ADVERTISERWhat Kind tf Voice^wLoud Speaker?Does ItafeRadioplied with. Compliance with them gives you asafe installation. Failure to follow them invitesunnecessary and totally avoidable risk. Furthermore,failure to comply invalidates your fireinsurance policies automatically.BOOK REVIEWA Home-Constructor's HandbookPRACTICAL RADIO CONSTRUCTION AND REPAIR.By James A. Moyer and John F. Wostrel.Published by the McGraw-Hill Book Company,Incorporated, New York. 319 Pagesand 157 Illustrations. Price $2.00.DoesItWKirve?orUoRegisterCleai: NaturalJfuman Tones ?Muterliberal guarantee you won't recognize you. -.SEE YOUR DEALERmiate. almost unbelievable improvement inistorted voice issuing from the speaker unitor SEND DIRECTDealers can easily secure Muter Product* for you from leading Jobbers.^_however,,ymjhave any difficulty in ohwill be made upon receu*.. - ,..-duce its utmost. Mail coupon today.LESLIE F. MUTER CO.76th O Greenwood AT... Dept. 822-N, CHICAGO. ILL.DEPENDABLE PRODUCTSThe complete Quality Popular Priced LineSend for comprehentioe catalogSet Builders!Be first to build the newMaenaformer 8-8 CircuitCommander-in-Chief olthe Air featured by RadioAuthority G. M. Beatin Sept. and Oct. Radio.Read his articles. See alsoSent, - and Oct. Popular10 and C. R. Call Book.MAIL COUPON NOWRadlart Lab. Co.. Otei. 57. l it. L " ', ChleaRo.Flense send me tree dencrlptive literature regarding Magnaformerperformance.NameAddress. .F.MUTER CO.76th & Greenwood Ave., Dept. 822-NChicago, III.D Send Muter Clarifier at once, postage prepaid.$6.00 is enclosed. U Send C. O. D.D Send ccaiplete Muter Catalog.NameAJJreuCtlu5tateIndependent Radio CorporationPrecisionManufacturers ofRadio Apparatus1516 Summer Street PhiladelphiaIFREE Log n.. >Call Book and Cat- .slog. Get your copy to-Send postcard no...day.American Auto a Radio Mfg. Co.HARRY SCHWARTZBBRO, PRKS.Depl. 123 Amencin Hidin Bldg.. Kllls Cily. MlWHOLESALE'Jlrrite for my Big 1928 Radio Catalogjust off the press. Thousands"marvelous bargains in nationallyadvertised goods. All theIt's aregular ,,ATEST IN RADIOS and.encyclope- luipment. Loweatwhole-diaon Radio.sale prices.All abou I Irouble llndAgentsWanted.NfiF-28'IRACTICAL Radio Construction and Repair"contains a potpourri of useful andpractical information. Its authors havecompiled their pages out of a large practicalknowledge and experience in set building. Thetitle implies a handbook of radio constructionand repairing a reference volume for thedealer's service man. It does not fail in thatrespect so much from incompleteness as it doesfrom poor arrangement. But it has much to commendit.The first part of the book deals with whatmay be termed the accessories of the radio receiverthe antenna, the vacuum tube and itspower supply, and, tucked away with these subjects,a chapter on the tool equipment needed forradio construction. Then follows a series ofchapters on radio-frequency amplifiers, describingseveral methods of controlling regenerationand including a few words about super-heterodyneamplification. Next follows a brief descriptionof systems of audio-frequency amplification.The subsequent few chapters deal with constructionaldetails. The first set to be describedin detail is the Browning-Drake receiver. Thewriters then again return to audio-frequencyamplifiers, presenting a strong case for a popularresistance-coupled amplifier kit. The superiorityof resistance coupling over transformer couplingis emphasized by means of a set of curves. Apparently,an inferior transformer and a superiorresistance amplifier were used as the basis of thetest. A chapter on impedance amplification,devoted to a description of the Thordarsonamplifier, follows that comparing resistance andtransformer coupling.Returning again to receiving sets, the authorsnext describe the "Universal," the Acme reflex,the Cotton super-heterodyne, and a short-wavereceiver. In general, these descriptions followclosely the conventional magazine style of exposition,with lists of parts, and details for assemblyand operation.No commercial receiversare described or even considered.The appeal of this book is confined generallyto the home constructor and his problems andnot to those of the dealer service man; an outstandingexception is the last chapter, where theservice man is suddenly remembered. This lastchapter makes interesting reading, containing, asit does, a fairly complete and practicalset oftroubles likely to be encountered in a radio receiverunder various conditions. A few biiefsamples are quoted to show the type of informationin this section:SET GIVES SQUEALING SOUND CONSTANTLY.-A constant squealing sound in a receiving set isgenerally due to a defective vacuum tube whuin the course of time has become soft or gassy.Continuous squealing mayalso be due to a verybadly run-down B battery or, to a less degree, toa worn-out C battery. A burned-out primary(Continued on page 416}

RADIO BROADCAST ADVERTISER 415Radio Is BETTER With Dry Battery PowerTransformersTwo additions to last year's Radio SensationThe Amazing Achievement inAudio AmplificationDesigned to fulfill the exactingrequirements of set builderswho demandmade to runthe/w// race /Y horse can make agood start But it takesreal stamina to finish!So it is with batteries. Stayingpower is the quality tolook for unfailing powerover a long period of service.Millions prefer BurgessChrome Batteries for just thisreason. They hold upThey last.Next time, buy black andwhite striped Burgess ChromeBatteries. You are certain toget longer and better servicefor your money.d)TOtTl6c^e P reserv *n g e 'e"ment used in leather,metals, paints and other materialssubject to wear, is also used inBurgess Batteries. It gives them unusualstaying power. Burgess ChromeBatteries are patented.cAik Any Radio EngineerBURGESS BATTERY COMPANYCentral Salts Office: CHICAGOCanadian Factories and Officts:Niagara Falls and WinnipegURGESSFLASHLIGHT & RADIOBATTERIESH. F. L. C-16 AudioTransformers and C-25output Transformer Neu;companions of a Qreat Unit,ivill work in any circuitand improve any radio set.H. F. L. FactsH. F. L. Units have beenused, approved and moathighly endorsed by RadioNews. Citizens Call Book.Radio Review, Radio Age.Radio Engineering. RadioMechanics, Chicago EoeningPost, the Daily News andothers. Thousands of engineersand fans, who haveturned to H. F. L. Units forbetter reception, hail themas the finest transformersknown to Radio unexcelledfor Power. Selectivityand Purity of Tone.Perfe, ctly matched, skillcarefullyfully designed.made, rigidly tested in aword, H. F. L. transformersare technically correctto the minutest detail.All H. F. L.. transformersare designed for baseboardmounting or invisible subpane!wiring each unit isenclosed and sealed in agenuine bakelite moulding.H. F. L. Units are easilyconnected into the assembly,simplify set construction,and make a beautifulfinished job.f EFFICIENCY ~[SENSITIVITY 3PRECISION AND1 HIGH QUALITY JThe new C-16 and C-25 Transformerswill work in any circuitand will improve any Radio Set.H. F. L. Units Give WonderfulClear ReceptionEngineers acclaim H. F. L. C-16 a marvellouslyefficient Audio Transformer. It carries signals athighest volume and lowest amplitude withoutblasting or developing harmonics. Operates withall power tubes as well as standard tubes.H. F. L. C-25 Output Transformer handles thevoltage output of power amplifying tubes, at thesame time matches the impedance of the averagespeaker to the tubes. Protects loud speaker unitwithout reducing plate voltage.Mechanical features of these two transformers are:A coil designed and treated to exclude moistureand withstand heavy electrical surges withoutbreaking down complete magnetic shielding toavoid interstage coupling terminals brought outso as to insure short leads.Endorsed by America's Leading EngineersManufacturersPRICESGuaranteed by theNo. H-210 Transformer $8.00No. H-215 Transformerg.OONo. C-16 Transformer8.OONo. L-25 R. F. Choke 5.50No. U41O R. F. Transformer 5.5ONo. C-25 Output Transformer8.OOSet BuildersDealersIf your jobber cannot supply you with H. F. L. Transformers, writeus for name of nearest jobber.HIGH FREQUENCY LABORATORIES131-M NORTH WELLS STREET, CHICAGO, ILL.

'My416 RADIO BROADCAST ADVERTISERBook ReviewPatternNo. 135RadioVoltmeterAQu alityInstrumentYour Radio Will BeBetterVoltmeter control of filament voltage will make any radioof balancereceiving set better. It enables you to retain that nicetyin filament emission, which brings in reception clear and exact withmaximum volume. It will prevent premature burnout of the radiotubes due to excessive filament voltage, for, with a voltmetermounted on the panel and connected to the filaments, you will knowat all times just what voltageisbeing applied to the filaments.The Jewell Pattern No. 135 voltmeter isgood looking andrigidly constructed and is the ideal instrument for filament control.The black enamelled case is two inches in diameter and contains aminiature, but very high grade, D'Arsonval moving coil type movement,which isequipped with a zero adjuster. Movement parts areall silvered and the scale is silver etched with black characters.The addition of this meter to your set will improve its appearancebesides being a great help to better and economical receptionWrite for descriptive circular''27radio instrument catalog No.No. Jj6 and ask for a copy of ourJewell Electrical Instrument Co.1650 Walnut Street, ChicagoYears Making Good Instruments'*winding of one of the transformers or a poorconnection in the jack connecting the loudspeaker and closing the battery circuits will alsocause this same effect.SET OPERATES WHEN PLUG OF TELEPHONERECEIVER Is PUT IN JACK OF DETECTOR CIR-CUIT, BUT DOES NOT OPERATE IN STAGES OFAMPLIFICATION. This difficulty may be due toreversed connections of the A battery, or theprimary winding of the audio-frequency transformerin the detector circuit may be burned out.No serious attemptis made to correlate thepractical information in this last section in amanner lending itself to easy reference.The set constructor will find much of interestin the book because it is, on the whole, reliableand accurate. We might pick out statementshere and there to quibble over, such as that inthe chapter on audio-frequency amplifiers.Speaking of audio-frequency transformers, theauthors say: "Some manufacturers claim thatthey can make transformers which amplifyconsistently over a wide range of wavelengths,"a correct, though rather unconventional way ofreferring to audio-frequencies. Another case ofa different kind: " If the sound volume from theloud-speakeris weak, tap the vacuum tubes witha finger nail to determine whether or not theaudio amplifiers are operating satisfactorily: ifthey are not, the tapping by the finger nail willcause a ringing sound in the loud speaker." Toinclude, in a final summary of testing instructions,so broad a generality, having so manyconceivable exceptions, is, to say the least,somewhat careless.A general criticism which may be made ofmany radio books is the superficial knowledge oftheir authors. Moyer and Wostrel are certainlyexempt from any such accusation because theyhave the outstanding virtue of knowing whatthey are talking about. But they have not metthe needs of service men working for the radiodealer; the authors' viewpointis that of theamateur set builder.The preferred circuits for home constructionare well selected and described; there are plentyof diagrams to browse among and, to one whoreads the book from cover to cover, many newfacts are likely to be discovered. Cut, if one wantsto find out in a hurry such a practical constructionalpoint as whether the; jack should be sowired that the sleeve or the tip of the plug goesto the B-plus lead, or the quickest way of findingsafely which tube is burned out with a set inwhich the filaments are wired in series, there isno telling if, how, and where the desired informationwill be found.EDGAR H. FELIX.Set Builders!-fc *n-^ij_Lbig 1928 Radio Cat- *Barry Ave., Dept. D, Chicago. JOHN E. FAST 8 CO. 3982 U. S. A. EQUITABLE INDUSTRIES ASS'N, RADIO DIV.All socket power devices must,^_J alojj, Call Book and TroubleFinder. 132 pages aboutdepend upon Condensers forsuccessful operation. Fast HiwfRadio. Chock full of newest circuitskits, transmitter parts, shortTeat Condensers have extracapacity and are built to withstandwave outfits, eliminators and speakers.every requirement Mill-Thousands of bargains at lowest wholesale prices.ions now in use and since 1919,A regular Radio Encyclopedia Frae. Write today.one of the oldest establishedAmerican Auto & Radio Mfg. Co.and reliable manufacturers,HARRY SCHWAKTZBRKG, PRES.Illustration shows condenser pack used in Q. R. S. or Pep*.Raytheon1Z5 American Radio Bldg., Kansas City, Mo.A-B-C unit. For perfect operation, build your A. B.C.picks with Fast condensers, whether specified, or not. Theylit all units.Features of Fast HI -Test CondensersCondenser life depends upon its dielectric strength. Fastcondensers have extraordinarily hitrh insulation resistance.By-pass condensers are all of the short-path type, affordingR U ONE?zero resistance to radio frequency curve. Absolutely noninductive.Co-operative membershipin E I A RADIO isAn rxrlusivp feature by-pasa condensers enclosed In onepiecedies-press steel housing, makes them positively imperviousto all climatic conditions or abuse. Before beingindustrious man in eachestablishing an honest,encased condensers receive special laboratory treatmentlocality in a successfulwhereby moisture content is effectually removed and onceradio industry of hisremoved, they stay that way, for the housing seals themown.permanently thereafter. That's why Fast Hi-Test condensersgive such excellent, dependable service.preferred. ApplyYoung marriedmenthe facts. Dealers Free condenser booklet brings and jobbers,by letter, giving thelend for pi ice list.name of your county, to350-B Broadway, New YorkUSE THIS COUPON FOR COMPLETE SETSRADIO BROADCAST SERVICE DEPARTMENTRADIO BROADCAST. Garden City, New York.Please send me information about the following manufacturedreceivers indicat:d by number:| Name1 Address(Number)(City)(Street)(State)ORDER BY NUMBER ONLYThis coupon must accompany each order. RB 1027

SingleControl7-TubeRETAIL PRICECompletely AssembledBIGGEST DISCOUNTS toAGENTS and DEALERSeither fullWORK or part time andmake big money. Tremendomadvertisingcampaign helps you sell. Regardlessof whether you have ever sold before,Test it withbesure to get our proposition. The Randolphsells on first demonstration. Menfor 3Dand women both can make money thiseasy way. Get your demonstration setfor thirty days FREE TRIAL.ELECTRIC OPERATIONIlluminated DrumSpace wound solenoidselected solid burl walnut. Bas-relief bronze escutcheonplates are mounted on the dial panel. In6-Tubedesign and appearance it is a cabinet worthy of thehigh-quality radio it contains. Solid walnut beautifullyshaped surrounds the soft verdi-greencontrol, six-tube radio.55panel.Nothing has beenspared to make the RandolphSeventhe leading radio receiver. We are so sure that it willsurpass even your b^st hopes that we know how safewe are in making the 3O day free trial offer.before you buy.Read What Owners SayMail Coupon NowI have logged more than 50 stations from coast tocoast. Lloyd Davenport, Littlefield, Texas. Retail Priceund unlimitedI have logged 52 stations from Cuba to Seattle theset is a world beater. J. Tampkinson, Detroit, Mich. SINGLEYour set is a revelation has all others tied to thepost for distance and selectivity. WaldoCONTROL .Powers,Vergennes, Vermont.On strength of its performance sold two more|Bets this week. T. Scanlow, Orlando, Florida.Beautiful AmpliphonicConsole SetRandolph Radio Corporation.711 West LakeMade of the finest carefully selected Street,solid walnut.Dept. 121Two-tone shaded finish. HasChicago, Illinois.built-in cone loudspeakerthat compares wi th any on the market and Send me fullaccurately reproduces high and low notes. Send forthe folder today that shows this beautiful console infull colors and gives complete details. Compareswith most table sets in price. For battery Nameorall-electric operation ready to plug inand tune in. Write for complete descriptions.AddressRandolph Radio CorporationState.711 W. Lake St. Dept. 121, Chicago, 111.POWERFUL seven-tube radio at factory price.-1-out spending a cent. We claim the Randolph Seven willout-perform any radio and we want you to satisfy yourselfthat it will. To do this, we will send you this powerful radio to trydays. Test it for distance, clearness, ease of operation, tone and everyother way you can. Unless it more than satisfies you, return it to us. EveryRandolph set must make good before it is sold.BatteryorThe Randolph Seven Is sold for use -with batteries or connected foroperation direct to electric light socket absolutely batteryless no chargers or batteriesjust plug in socket and tune in. 100% efficient either way. Its construction andperformance have been tested and approved by leading radio engineers and authorities andleading radio and scientific publications.Single ControlOne drum dial operated by one simple vernier control tunes in all stations with easy selectivityto tremendous volume. No overlapping of stations. Illuminated drum permits operationin the dark. Volume control for finer volume modulation. This is a 7-tube tuned radiofrequency receiver with power transformers and power amplification.coils Full and completely shielded. A real receiver of the highest quality. Tremendousdistance, wonderful tone quality, simple to operate.The Randolph cabinets are in themselves beautiful pieces of furniture made of carefully7hePandoltthNow yon can have a new, modem, single-Do not con.parethis set with old style 2-dial 6-tube seta s,-ll-HIK for about the same price. The RandolphlltL'.s Sfru..r Six has also been tested and approvedby the leading: radio engineers.Cornea in a beautiful solid walnut cabinetoJ hand -rubbed finish. Single control.Illuminated Drum with apace for logging.Absolutely dependable and very selective.Sent for 3O Days Free Trial. You test ItThe Randolph Radio Corporation are pioneersin the manufacture of radios. All of its vastresources have been UBed inmaking and perfecting of the Randolph Receivers.Because of our long and successfulexperience in the radio business, we are perfectlyconfident in Bending out a RandolphRadio on trial. We know what it will do.Mail us the coupon now for the greatestradio offer ever made.USE THIS COUPON TODAY!particulars about the RANDOLPH Six andSeven -Tube Table and Console Sets with details of your30 Day FREE Trial Offer.CityMark here () if interested in Agent's proposition.

THE COUNTRY LIFE PRESS, GARDEN CITY, NEW YORKPlug In-and Tune la30A*Real Electric)SetThree Year GuaranteeShipped direct from our factory atrock bottom prices cost less thanmost battery setsNo Batteries, Chargers or EliminatorsNo Acids; No Liquids Plug In Press But ton "Tone In*AGENTS! DEALERS!)BIG PROFITS!Make big money taking orders for Idynes. AH or part time. Metrodyne _Electric Radios are in a class by themHselves* Unequalled for quality, performancand price. Demonstrate at home and takorders. Lowest wholesale prices. Yodemonstrating set on 30 days' free \Mail coupon below for details.Gorgeous ConsoleElectric RadioHere is the Mctrodyne All Electric ConsoleRadio a gorgeous, genuine walnut cabinet,in a beautiful two-tone finish. Has a built-ingenuine Metro-Cone large size speaker. Bringsin programs with great volume, reproducing theentire range from the lowest to the highest noteswith remarkable clearness and distinction. Allmetal parts are finished in old gold. Wonderfulelectric radio, in a cabinet that will beautifythe appearance of any home.fitrodALL ELECTRIC RADIO7 Tuhes Single Dial Set100% Electric RadioAt last I The radio you've dreamedabout ! If you have electricity in your homeyou can now really enjoy coast to coastradio reception without the care, bother andmuss of batteries, chargers, eliminators, etc.The Metrodyne All Electric is a real, genuinebatteryless radio set. Simply insert theplug in the socket, press the switch buttonand "tune in." You could not possibly buy abetter radio set than the Metrodyne AllElectric, no matter what price you paid.BEAUTY EFFICIENCYDEPENDABILITYThe Metrodyne All Electric Radio isa 7 tube, single dial set. Only the highestquality low loss parts are used throughout.Solid walnut cabinet, beautiful two-tone effect,with handsome gilt metal trimmings.Size of cabinet, 28 inches long, 13 inchesdeep, 10 inches high. Has electrically lighteddial so that you can log stations in the dark.Only one dial to tune in all stations. Excellent tone qualities wonderful volumevery selective.CostsLess Than Most Battery SetsDo not confuse the Metrodyne electric radio with ordinary lightsocket sets, because the Metrodyne is truly an all electricradio consumes less than 2c worth of power a day.Comes to you direct from the factory. Its low costbrings it down to the price of an ordinary batteryset. We are so confident that you will be delightedwith this wonderful, easy-to-operatebatteryless radio that we offer toship it to your home for thirty days*free trial you to be the judge.Mail This CouponWe are one of the pioneers of radio. Thesuccess of Metrodyne sets is due to our liberal30 days' free trial offer, which givesyou the opportunity of trying before buying.Thousands of Metrodynes have beenbought on our liberal free trial basisWRITE TODAY!METRO ELECTRIC COMPANY2165 N. California Ave. Dept.6O7, Chicago, Illinois*%&l&!j*C'l^'